Source: http://www.wired.com/science/discoveries/magazine/17-08/st_best
1 Sea mammal blowhole. Any animal that spends appreciable time in the ocean should be able to extract oxygen from water via gills. Enlarging the lungs and moving a nostril to the back of the head is a poor work-around.
2 Hyena clitoris. When engorged, this "pseudopenis," which doubles as the birth canal, becomes so hard it can crush babies to death during exit.
3 Kangaroo teat. In order to nurse, the just-born joey, a frail and squishy jellybean, must clamber up Mom's torso and into her pouch for a nipple.
4 Giraffe birth canal. Mama giraffes stand up while giving birth, so baby's entry into the world is a 5-foot drop. Wheeee! Crack.
5 Goliath bird-eating spider exoskeleton. This giant spider can climb trees to hunt very mobile prey. Yet it has a shell so fragile it practically explodes when it falls? Well, at least it can produce silk to make a sail. Oh, wait it can't!
6 Shark-fetus teeth. A few shark species have live births (instead of laying eggs). The Jaws juniors grow teeth in the womb. The first sibling or two to mature sometimes eat their siblings in utero. Mmm ... siblings.
7 Human stomach. People can digest a lot except for cellulose, the primary component of plant matter. Why don't we have commensal bacteria in our guts to do it? They're busy helping termites.
8 Slug genitalia. Some hermaphroditic species breed by wrapping their sex organs around each other. If one of said members gets stuck, the slug simply chews it off. What. The. Hell?
9 Quadrupeds. Let's say you're a four-footed animal. Now let's say you get a wound on your back, or an itch, or a bug wandering up there. Tough luck, kid. You probably can't do much about it. Hope there's a low branch around.
10 Narwhal tusk. The unicorn-like protuberance on a male narwhal's head is actually a tooth that erupts through the front of the jaw and keeps on growing, up to 9 feet. Narwhal: "Doc, I have a toothache." Dentist: "Indeed."
