Our 25 Most Popular Stories of 2021

Here at Mental Floss, we take our reputation of being the internet's home for all things curious very seriously, even—and perhaps most especially—when we're sharing a story like this one about an enterprising sixth-grader who devised an experiment in order to determine whether a cat's butthole actually touches everything it sits on (note: it involves red lipstick). Which is why, at the end of each year, we're always fascinated to see which stories most connected with our readers in the previous 12 months.

After pouring over the biggest stories of 2021 (which are different from our favorite stories of 2021, though there's definitely some overlap), some key takeaways might be that Mental Floss readers adore their pets and all their bizarre behaviors, are fascinated by the features they see on other motor vehicles while driving, love a good shark tale, and really want to know what happened to all that white dog poop they used to see. So buckle up for a wild ride back through the most popular stories of 2021.

1. The Reason Service Vehicles Like Ambulances and Fire Trucks Have Chains Hanging From the Bottom

Like a cat on a perch, the chains on school buses and ambulances seem to dangle with no apparent purpose. Their true mission is actually pretty clever.

2. 12 Incredible Facts About the Sutton Hoo Ship Burial Treasure

The Sutton Hoo ship burial, one of the most important archaeological discoveries in British history, contained a hoard of Anglo-Saxon artifacts that transformed our understanding of the 'Dark Ages.'

3. What Happened to the White Dog Poop That Used to Be Everywhere?

It wasn't a product of your young imagination: Chalky, white dog poop really was everywhere in the 1970s and '80s. Here's why it went away.

4. Why Do Semi Trucks Have Spikes On Their Wheels?

A semi truck's tire spikes mainly protect the wheels’s lug nuts. They also offer drivers a chance to give their trucks a bit of personality.

5. 30 Fascinating Facts About Farts

From the fart jokes penned by famous writers like Shakespeare to the horrifying consequences of holding in your flatus, here's everything you ever—and never—wanted to know about farts.

6. Going Fishing: When Universal Studios's Jaws Ride Terrorized Park Guests

The original Jaws ride at Universal Orlando closed after two months—but not before terrorizing theme park guests (and their children).

7. 10 Pieces of Playground Equipment that Nearly Killed Your Grandparents

These vintage playground devices were so perilous, kids of yesteryear were lucky to live through recess.

8. How Disney's Frozen Led to a Breakthrough in Russia's Dyatlov Pass Mystery

Sixty-two years ago, nine hikers died in what's now Dyatlov Pass in Russia after fleeing their tent for unknown reasons. Using models inspired by Disney's Frozen, scientists have come up with an explanation for the incident.

9. The 25 Greatest Revenge Movies of All Time

As Khan Noonien Singh once said, “revenge is a dish best served cold,” and cinema is filled with stories where vengeance and retribution gets served with chilling brutality and precision. Here are 25 of the best of those tales.

10. James Baldwin's Record Collection Is Now a 478-Track Spotify Playlist

The celebrated author of Go Tell It on the Mountain used music to inspire and influence his work. Now you can listen, too.

11. The 10 Worst Presidents in American History, According to Historians

According to historians, these are the worst American presidents ever to hold the highest office in the land.

12. The Real Reason Cars Have Those 'Grab Handles' Above the Doors

This particular car safety feature isn’t so your passengers can wordlessly convey that they think you’re a reckless driver.

13. The 30 Greatest Action Movies of All Time

The action movie genre is packed with plenty of masterpieces, but these 30 films are our absolute favorites.

14. Why Do Dogs Steal Your Spot on the Couch as Soon as You Get Up?

Dogs that rush to fill the space on the sofa may be doing it because they love you, or because they want to be top dog. Here's how to tell the difference.

15. Zak Bagans Shares 16 Behind-the-Scenes Facts About Ghost Adventures

For more than a decade, Ghost Adventures has been spooking up the airwaves of the Travel Channel, "capturing groundbreaking proof of the paranormal" on camera in hundreds of haunted destinations around the globe. Now Zak Bagans is sharing some of the show's behind-the-scenes secrets.

16. Why Do Marathon Runners Poop Their Pants?

To be an endurance runner is to leave a trail of sacrifice behind you. Here's why marathoners sometimes get off to a runny start.

17. 11 Songs Inspired by J.R.R. Tolkien’s The Lord of the Rings

Thanks to Led Zeppelin, there is nothing more rock ‘n’ roll than Gollum slipping away with your girl.

18. Why a King’s Wife Is the Queen, But a Queen’s Husband Isn’t the King

At 133 words long, Prince Philip’s full title included the words duke, earl, baron, royal knight, and just about every other noble designation you can think of. But the highest and perhaps most obvious moniker that was conspicuously missing: king.

19. 11 Actors Who Took Home Their Animal Co-Stars

Animals in movies seem lucky to begin with—but none can compete with the shelter dog that Chris Evans took home.

20. Brown Eggs vs. White Eggs: What’s the Difference?

The color of an egg's shell says nothing about its quality. The only difference between brown eggs and white eggs lies in the breed of the chicken that laid them.

21. The 20 Longest-Running TV Shows of All Time

From daytime soap operas to late-night comedy programs, these are the longest-running TV shows in entertainment history.

22. Why Lining Your Flower Pots With Coffee Filters Makes Houseplants Harder to Kill

If you have a bad habit of over- (or under-) watering your houseplants, a coffee filter inside your flower pot can be a safeguard against both issues.

23. The Real People Who Inspired 21 Popular Songs

Contemporary music has become a constantly expanding repository of classics whose origins sprung up from the most painful and profound experiences, the relationships that dominated portions of the artists’ lives, or just chance encounters that lodged in their memories and touched their souls.

24. Why Do Cats Head Bump Humans?

Cats seem to enjoy booping humans on their foreheads. Is it a sign of affection, or yet another sign of condescension?

25. When a Captive Shark Vomited Up a Human Arm—and Sparked a Murder Investigation

In 1935, a tiger shark on display at the Coogee Aquarium in Sydney, Australia, regurgitated a human arm. The strange incident was just the beginning of one of the country's most twisted murder cases.