1. Hummingbirds can fly backwards.
4. When caterpillars metamorphosize, they digest themselves into a "soup," then reform into a butterfly.
5. Female insects of the genus Neotrogla have a penis and can have sex for up to 70 hours.
6. There's a mammal in Australia that has sex until it disintegrates.
7. During sex, flies create a buzz that can attract predatory bats.
8. Female black widow spiders sometimes kill and eat their male counterparts after mating.
9. Female komodo dragons don't need a male to reproduce.
16. Armadillos found in the U.S. nearly always give birth to identical quadruplets.
17. Elephants are pregnant for almost two years.
18. They're also believed to grieve for their dead.
19. Penguins have knees.
20. Wombat poop is cube-shaped.
21. Guinea pigs are neither pigs nor from Guinea.
22. Koala bears aren't bears: They're marsupials.
24. Ostrich kicks can kill a human.
25. Male platypuses are venomous.
26. An octopus has three hearts.
27. Horned lizards can shoot blood out of their eyes to defend themselves.
28. Mantis shrimp have four times as many color receptors in their eyes as humans do.
29. Catfish use their entire bodies to taste things.
30. You can use a blue whale's wax earplug to work out its life history.
31. Dolphins can stay active for 15 days or more by sleeping with only one half of their brain at a time.
32. Some lobster species can live to be 50 years or older.
34. The Chinese soft-shelled turtle can expel urea, the main waste product in urine, out of its mouth.
36. Each of a tarsier's eyeballs is as big as its brain.
41. While moms hunt, emperor penguin dads fast for weeks and protect their egg from the cold with a special flap of skin.
42. Grizzly bear dads sometimes kill cubs, so moms find dens that are far away from males.
44. Tardigrades are the only animal we know of that can survive in the vacuum of space.
45. Giraffes have sturdy hearts and high blood pressure, which help prevent fainting when they lift their heads from the ground to the sky.
46. Aging male giraffes go black instead of gray.
47. And that feeling you get when something is so cute you can't help but want to squeeze it hard is called "cute aggression."