During a long flight, have you ever idled away the hours by taking a closer look at the aircraft cabin? If so, you might have noticed some unique and unusual details. For instance, unlike windows found elsewhere, the windows on an aircraft are oval instead of square. Find out why that is and the significance of that tiny hole you see at the base of each window.

Aircraft Windows Haven’t Always Been Round

Introduced during the early days of commercial aviation, the De Havilland Comet was a pioneering British plane that was the first to be fitted with jet engines. In contrast, rival planes at the time, such as the Lockheed Constellation, were powered by propellers. The Comet, launched in 1952, flew at higher altitudes and faster than its predecessors. When it first went into service, the Comet had square windows. Though no one knew it at first, this would prove to be a devastating flaw.

At first, there were no issues with the Comet, but as the planes racked up more mileage, fatigue fractures started to appear. Several Comets crashed, including one that plunged into the Mediterranean Sea on January 10, 1954, shortly after takeoff from Rome. When experts inspected the wreckage, they noticed that an 8-foot-long fracture had occurred in the corner of one of the windows that was positioned where the radio aerials were located, impacting another window frame and contributing to the breakup of the fuselage after takeoff.

Improving Airline Safety

Throughout the history of commercial aviation, investigators have used the knowledge gained from the findings in the aftermath of plane crashes to inform changes that should be made to improve safety. Though metal fatigue was officially the cause of those early De Havilland Comet crashes, the square design of the windows, coupled with the pressurized cabin, was considered a contributing factor. 

As a direct consequence of those tragic early crashes, Comets were grounded indefinitely, until they could be retrofitted with oval windows to resolve the problem of stress concentrations at the corners. Not only is a rounded shape stronger, but this new design was also better able to withstand the differences in pressure found on the inside and outside of the aircraft. (Aircraft cabins are pressurized to ensure the concentration of oxygen is high enough for us to breathe while traveling at high altitude.)

What Are the Tiny Holes for in Aircraft Windows?

The rounded shape of the windows you see on modern airplanes isn’t the only important aspect of their design. The internal layers you see on the window beside you are made of acrylic rather than glass. Look closely, and you’ll see a tiny hole in the nearest of the three layers. It’s known as a bleed hole or a breather hole. Though tiny, it plays an important part in keeping us safe while we’re in the air. 

Because air pressure varies with altitude, plane windows need this tiny hole to allow sufficient air to pass through in order to equalize the pressure. The stress remains greatest on the outside, which prioritizes passenger comfort and safety. If there was no hole, the outer pane could theoretically crack or even pop out completely. The hole’s secondary function is to prevent frost or condensation from building up, so it helps to ensure you always have an unobstructed view of what’s outside the window.

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Navigating the intricacies of Transportation Security Administration (TSA) regulations can be a hassle for even the most seasoned travelers. To keep airport security lines moving (and to keep all your toiletries with you), it’s important to understand the 3-1-1 rule for liquids in carry-on bags. The TSA sets these regulations for liquids in carry-on baggage to ensure safe and efficient air travel. While they may seem strict, the guidelines are straightforward once you understand them (along with a few important exceptions). Below, you’ll find everything you need to know about TSA liquid rules before your next flight.

The 3-1-1 Rule

The TSA’s 3-1-1 rule is a simple way to explain how many ounces of liquids each passenger is allowed in a carry-on bag.

• 3: Each liquid must be in a container of 3.4 ounces (100 milliliters) or less.
• 1: All containers must fit inside a quart-sized clear plastic bag.
• 1: Each passenger is allowed one such bag.

Keep in mind that the 3.4-ounce rule applies to the size of the container. “Ultimately, the size is determined by what is written on the bottle itself,” the TSA says — the amount of actual liquid in the bottle doesn’t matter. Any bottle larger than 3.4 ounces, regardless of its contents, must be checked or thrown away. While there are no limitations on liquids in checked baggage, consider placing them in leakproof bags to avoid mid-flight messes.

Thankfully, it’s easy to find TSA-approved refillable toiletry containers and quart-sized travel bags to pack in your carry-on. This can help ensure your liquids are within TSA size standards.

What Counts as a Liquid?

The 3-1-1 rule isn’t only for traditional liquids, such as water and drinks. It applies to anything that isn’t solid, including aerosols, oils, gels, creams, lotions, and pastes. This includes most toiletries, such as shampoo, sunscreen, body wash, hair gel, hair spray, toothpaste, skin care, aerosol deodorant, and liquid makeup. 

It also includes some food. Even if the product is factory-sealed, you cannot bring any food that isn’t solid — such as peanut butter and salsa — through security. The rule even applies to souvenirs purchased during your trip (before security) that might contain more than 3.4 ounces of liquids, such as bottles of wine, snow globes, and even Magic 8 Balls. These items need to be placed in checked baggage.

Solid yet spreadable items — such as stick deodorant, bar soap, lipstick, and powder makeup — are not considered liquids and don’t need to be packed in your quart-size bag.

Exceptions to the 3-1-1 Rule

There are a few notable exceptions to the liquid rules, most often made for medical and health reasons. For example, the TSA says larger amounts of medically necessary liquids, gels, and aerosols (in reasonable quantities) are permissible in carry-ons, so long as you declare them to the TSA officers at the security checkpoint. This includes prescription and over-the-counter liquid medications (such as cough syrup or insulin), IV bags, and ice packs or gel packs. The officers will assist you by inspecting them separately. 

Other exemptions to the 3.4-ounce rule include food for infants, such as formula and breast milk. For toddlers, sippy cups filled with water or juice and pouches of pureed food in excess of 3.4 ounces are permissible — just inform the TSA agent at the beginning of your screening process and remove the items from your carry-on bag.

What About Liquids Purchased After Security?

Any liquids or semi-liquids purchased after the security checkpoint, regardless of size, are allowed on the plane because they pass rigorous safety checks. This includes items such as coffee, water, snacks, and souvenirs.

It also includes duty-free liquid purchases made at a duty-free store in the terminal. According to the TSA, you may carry more than 3.4 ounces of fluid in your carry-on bag if you meet these three requirements:

• The duty-free liquids were purchased internationally while you were traveling to the U.S. on a connecting flight.
• The liquids are packed in a clear, tamper-evident bag by the retailer and do not show signs of tampering.
• The purchase was made within the last 48 hours, and you have the receipt.

Prohibited Liquids

Certain liquids and nonsolid items are always prohibited in carry-on and checked baggage due to safety concerns. This includes flammable aerosols, such as spray paint and spray starch (fabric wrinkle remover), as well as compressed gas cartridges, like CO2, which are used for inflating bicycle tires. Similarly, self-defense sprays (mace or pepper spray) are banned in carry-ons but are permitted in amounts of up to 4 ounces in checked luggage.

Hazardous liquids like those used for cleaning (e.g., bleach, pesticides, and drain cleaner) are also banned from U.S. flights. Lastly, alcoholic beverages with more than 70% alcohol (over 140 proof) are prohibited from carry-on and checked luggage; this includes grain alcohol and 151-proof rum.

International Liquid Rules

Most international security organizations stick to similar liquid regulations to streamline the travel process. For instance, in the European Union, the maximum size per container is 100 milliliters (approximately 3.38 fluid ounces), and all carry-on liquids must fit into a 1-liter clear bag (which is roughly the same size as 1 U.S. quart). The EU makes similar exceptions for medical liquids, infant food, and duty-free purchases.

Meanwhile, LATAM Airlines, South America’s largest airline, permits various quantities of liquids in carry-on baggage according to guidance from local authorities. Those traveling through security in Brazil, for instance, may bring up to four containers of liquids, each containing 300 milliliters or less. For travelers going through security in Chile, Peru, Colombia, and Ecuador, there are no restrictions on the quantity of carry-on liquids. For all other international flights, LATAM adheres to the 3-1-1 rule used in the U.S. and European Union.

Whether it’s coffee or alcohol, people enjoy various beverages all across the world. They do so in different ways, of course, and nearly every country has its own traditions. For example, ordering Guinness in Ireland comes with unwritten rules, as does sipping sake in Japan. No matter where you’re traveling, it’s best to do a little research on local drinking culture before your next trip. Here are a few interesting and unexpected drinking etiquette tips around the world.

Ordering Cappuccino in the Afternoon – Italy

As anyone who’s ever seen those viral videos of people breaking spaghetti in front of aghast Italians already knows, food is a way of life in Italy. This is equally true of coffee, which is unsurprising when you recall how many forms of it originated there: espresso, macchiato, and cappuccino, to name just a few. 

If you try to order a cappuccino after 11 a.m. in Rome, however, you may get a funny look. It’s considered a morning drink due to the milk, and is usually consumed relatively quickly alongside a pastry or croissant. (Traditionally, breakfast in Italy is sweet rather than savory.)

Espressos and macchiatos, meanwhile, are meant to be savored and don’t have (much) added milk and sugar. This is rooted in practical concerns, as milk is considered difficult to digest — making it more suited to the morning, when your body has more time to process it.

Clinking Glasses – Hungary

In many countries, it’s customary to touch glasses when toasting. Not so in Hungary, where this is a faux pas dating back more than a century and a half. It began in 1849, when the Austrians are said to have celebrated a military victory against Hungary by clinking beer glasses. (The story is likely apocryphal, but that’s never stopped a tradition from forming in the past.) While generally Hungarians aren’t opposed to clinking glasses for wine or cocktails, they uphold the legacy of not doing so with beer.

Pouring Your Own Drink – Japan and South Korea

Whether it’s soju in South Korea or sake in Japan, drinking is a key social activity in both countries — and, as such, comes with unwritten rules. One of the most important is not to pour your own drink. Instead, you should wait for others to pour for you. In turn, you should pour their drinks for them. In Japan, this is known as shaku suru or kumu.

There are even more specific rules when drinking with elders in South Korea, namely holding your drink with both hands while they pour for you and turning your body away from them when taking a shot.

Not Maintaining Eye Contact – Denmark and Germany

The next time you find yourself raising a glass in Denmark or Germany, be sure not to break eye contact with your host. It’s considered poor form to do so — especially in Germany, where those who don’t observe this tradition may be cursed with seven years of bad sex.

Leaving Half-Full Glasses on the Table – Russia

Vodka is an integral part of the culture of Russia, where the average person is said to down around 17 shots per month — more vodka per capita than any other country in the world. As you might expect, there are a number of customs to go along with all that history. For starters, Russians don’t actually say, “Na zdorovye!” (nuh zdah-ROHV-yeh) when toasting. They don’t have a single equivalent to “cheers” at all; instead, they use different phrases on different occasions. 

Just as importantly, proper etiquette is to down your entire shot in one go. Don’t put a glass on the table unless it’s empty, and place empty bottles on the floor rather than on the table. And as harsh as some consider the taste of vodka, in Russia, it’s almost always consumed neat rather than mixed.

Not Buying Your Friends a Round – Australia and Ireland

Should you be lucky enough to drink Guinness in an Irish pub anytime soon, don’t just buy one for yourself — get a round for everyone you’re with. According to tradition, the rest of your group will reciprocate your good deed. It’s simply how it’s done in Ireland, and in Australia, where buddies taking turns buying rounds is called shouting.

Not Deferring to Your Elders – China

Chinese drinking culture can be summed up by a famous proverb that translates loosely to, “With a close friend, a thousand cups of wine is far too little.” Another important term is “ganbei,” which means “empty cup” and is used for toasting. 

But, as in many aspects of Chinese culture, respecting one’s elders is of the utmost importance when drinking. For starters, never raise your own glass higher than theirs when clinking glasses during a toast. And if you’re toasting several people during a special occasion, start with the oldest person first.

When we think about travel hygiene, most of us focus on places like airport restrooms, hotel remote controls, and airplane tray tables. But there’s a frequently overlooked place that deserves a spotlight: the rental car. With over 108 million Americans expected to rent vehicles annually by 2027, these cars may be teeming with germs from countless travelers. Sure, that freshly vacuumed floor and pine-scented air freshener might suggest cleanliness, but looks can be deceiving. Beneath the surface, rental cars can harbor unwelcome souvenirs — hidden pockets of grime and bacteria — sometimes in places you’d least expect.

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Myth Busting: It Isn’t the Steering Wheel

The steering wheel is a high-contact zone, so it’s only natural to assume it must be one of the dirtiest places in a car. According to a consumer survey, U.S. drivers believe the top three germiest places in a car are the steering wheel, driver’s door handle, and gear shift. However, this isn’t entirely accurate. 

Researchers at CloroxPro found 408 germs on the steering wheel, while another study from the microbiology team at Aston University in the U.K. identified 149 bacteria. This might sound like a lot, but it’s less than half the amount of bacteria and other germs found in the dirtiest parts of a rental car. So, what are the germiest spots? Let’s take a look below.

Dirtiest Places in a Rental Car

According to the University of Aston, the dirtiest locations in a car had a bacterial contamination level equal to or exceeding what you’d expect to find on the average toilet seat or handle, and there is one spot that is a bacterial bullseye: the trunk. In the university’s study, 1,425 bacteria were identified in the trunk, the most of any place swabbed. The Clorox team found that the trunk had the second-highest levels of contaminants, with 1,180 germs. (The driver-side floor mats were found to have the most germs in their study.) 

Other highly contaminated areas in the Clorox study were the front seat cup holder (1,179 germs) and the dashboard air vent (1,082 germs). Aston University also found similar issues with the dirtiness of dashboards due to their high-touch controls. The university further revealed that the driver’s seat had twice the levels of bacteria as the back seat (649 vs. 323). 

Surprisingly, the gearshift had nearly three times the amount of bacteria (407) as a steering wheel (146), suggesting that while steering wheels are cleaned often, gear shifts are overlooked. 

Should You Be Worried?

While it’s not cause for significant concern, the microscopic dangers potentially lurking in your rental car might be something you consider during your next trip. “Based on our research, almost everyone agrees that a clean and sanitized car makes you feel better, but consumers rarely think about the germs in their cars and the impact they can have on their health,” Lynda Lurie, director of marketing at CloroxPro, said in the study. 

When in doubt, take a few minutes before you start driving to sanitize high-touch zones in your rental car using travel-friendly disinfectant wipes. Along with wipes, you may wish to pack hand sanitizer and a small trash bag to create a rental car hygiene station.

As far as deep cleaning goes, major rental car companies such as Enterprise and Hertz guarantee that their cars are cleaned between every customer. Enterprise, for instance, has a “Complete Clean Pledge,” which promises to sanitize more than 20 high-touch points, including all the dirtiest areas we already mentioned, such as control buttons, gear shifts, cup holders, and more. But if you’re concerned about the cleanliness of your rental car, don’t hesitate to reach out to your rental agency directly before you hit the road. 

About the data: To determine the grossest parts of a rental car, we looked at two studies. The first was conducted by a team of U.S. researchers at CloroxPro, whose swab tests measured levels of bacteria, yeast, and mold — all of which can impact your health while traveling. The second study was conducted by a microbiology team from Aston University in the U.K., who swabbed only for bacteria, such as E. coli and Staphylococcus.

Featured image credit: Olga Pankova/ Moment via Getty Images