Why do female sharks have thick skins? How many bones are in your body? What color are the eyes of a scallop? What did people do before there was toilet paper?
Find out the answer to these questions and more in this offbeat list of fun facts in science and history.
Editor’s Note: This list was originally published in 2013. It was updated with new information in March, 2016.
Female sharks have thicker skins than males. Scientists think it's because males have this odd tendency to bite females while mating. Despite this, sharks sometimes still gather in large quantities. In February 2016, researchers reported that more than 10,000 blacktip sharks were lurking together off the Florida coast. Understandably, though, pregnant female sharks seem to avoid males on migration routes. Who wouldn't?
Next: That's deep!
The ocean is 12,080.7 feet (3,682.2 meters) deep on average. That's about eight Empire State Buildings, stacked one on top of the other. The deepest part of the ocean, however, is about 36,200 feet down (11,030 m). That's more like 25 Empire State Buildings.
Next: A weird but handy fact . . .
Look at the back of your hand and extend your thumb. See those two little tendons pop out and form a triangle between your wrist and your first thumb joint? Scientists call that triangle the "anatomical snuff box," because people used to have the habit of sniffing powdered tobacco from this fleshy depression.
Next: Early toilets
Speaking of necessities, residents of ancient Pompeii could go upstairs to pee. Though the eruption of Mount Vesuvius in A.D. 79 destroyed many second stories, pipes left behind reveal traces of fecal matter, and the occasional upstairs toilet still remains in the ruins.
Next: Facts to bone up on
The adult human skeleton has 206 bones. The smallest is the stapes or stirrup, the innermost of three bones in the middle ear; the femur (thighbone) is the longest and strongest, and the tibia in the lower leg is the second largest in the human skeleton. What you may not know is that babies are born with about 270 bones. Some fuse together as their bodies grow.
Next: How a cockroach hisses
How did the Madagascar hissing cockroach got its name? Well, it hisses, of course. But how it hisses is a little weird. The giant insect forces gas through tiny breathing pores called spiracles on its thorax and abdomen. The cockroaches hiss when surprised, when challenging other cockroaches to a fight and when trying to attract mates.
Next: What you'd weigh on the moon
Gravity on the moon is a sixth of what it is on Earth. Someone who weighs 150 pounds (68 kg) on this planet moves the scales at only 25 pounds (11 kg) on the moon. Its gravity is so much lower because the moon is just 1 percent the mass of Earth. Your weight on the various planets would vary greatly. If you could stand on Jupiter, you'd weigh more than twice as much.
Next: Before there was toilet paper . . .
Toilet paper is a relatively recent invention, but the ancients still had to wipe. Roman philosopher Seneca, who lived from 4 B.C. to A.D. 65, recorded the use of a sponge attached to a stick that did the job. Between uses, the tool (called a tersorium) sat in a bucket of salt water or vinegar water.
Next: How much can a camel drink?
Camels can down 30 gallons (113 liters) of water in just 13 minutes. The water is stored in the camel bloodstream, while the fatty hump. Rather than being stored in its fatty hump serves as a source of nourishment when food is scarce.
Next: That's a long tongue!
The Central American salamander Bolitoglossa dofleini can extend its tongue more than half its body length in 7 milliseconds, 50 times faster than you can blink an eye.
Next: The hottest spot on Earth
On Sept. 13, 1922, the mercury soared to 136 degrees Fahrenheit (57.8 Celsius) in El Azizia, Libya. Scientists say this is the hottest temperature ever recorded on the planet, though higher temperatures might have occurred in places where there are no measuring stations.
Next: What you're full of . . .
The human body is full of friendly bacteria, with organisms on our skin and in our guts helping keep our bodies humming. Breast milk alone can have up to 700 species of bacteria, according to a study released in January 2013.
Next: How a platypus could easily kill a dog
The male platypus has a venomous spur on its hind foot capable of dispensing a poison that can kill a medium-sized dog.
Next: Yes, you can put a dead pope on trial
The Catholic Church once put a dead Pope on trial. After Pope Formosus died in A.D. 896, his successor had him disinterred, dressed in papal robes and set up to face a laundry list of political charges. The cadaver lost.
Next: You think you have trouble remembering faces!
Prosopagnosia is a disorder in which people struggle to recognize faces. Faces are so important that humans have a brain area called the fusiform gyrus that specializes in recognizing them. Developmental problems or injuries to the fusiform gyrus can leave people clueless about the looks of even loved ones.
Next: Mighty little shrimp
Mantis shrimp can use their armored claws to strike at speeds of 74 feet per second (23 m/s), delivering blows with 200 pounds (91 kg) of force behind them. The crustaceans are only about 4 inches (10 cm) long. Guess how they earned the nickname "thumb-splitters?"
Next: A creature with 100 eyes
Scallops have as many as 100 simple eyes. They're frequently blue.
Next: You'll be surprised how much blood is inside a pregnant woman's body . . .
When a woman gets pregnant, she's not only growing a baby — she's growing a support system for that fetus. As a result, pregnant women have about 50 percent more blood by week 20 of pregnancy than they did before they conceived.
Next: This human heart is more than 800 years old . . .
King Richard the Lionheart's heart is still around. After the English monarch died in 1199, his heart was removed and preserved — though today it's basically just a pile of dust.
Next: A 30-foot neck
The dinosaur with the longest neck for its body size is Mamenchisaurus hochuanensis, a sauropod dino that lived in what is now China. The American Museum of Natural History in New York has a Mamenchisaur specimen with a 60-foot-long (18 m) total length, a whopping 30 feet (9 m) of which is neck.
Next: A metal that's liquid but not hot
Mercury is the only metal that is liquid at standard room temperature and pressure. That's because the electrons that spin around the nucleus of a mercury atom have just weak links or bonds with other mercury atoms at room temperature, keeping the metal in a liquid state, according to the Discovery Channel.
Next: The oldest bra?
Modern bras didn't come into fashion until the corset fell by the wayside in the late 1800s. But researchers poking around in a scrap pile in an Austrian castle have found linen bra-like garments dating back 600 years.
Next: A creature with no stomach
Seahorses don't have stomachs, just intestines for the absorption of nutrients from food. Food passes through their digestive system rapidly, so they eat plankton and small crustaceans almost constantly.
Next: The smell of rotting flesh
Amprophophallus titanium blooms with clusters of flowers that can reach 10 feet (3 m) in height. But these petals smell so much like rotting flesh that the plant is known as the "corpse flower."
Next: Shut your trap. Quickly!
Carnivorous, bog-dwelling plants called bladderworts can snap their traps shut in less than a millisecond, 100 times faster than a Venus flytrap.
Now what? See our 50 Interesting Facts about Earth.