Echidnas are one of those weird Australian animals that seems to have been pieced together from leftover bits of other animals. Mammals that lay eggs, echidnas are covered in pointy hedgehog-like spines, but with a long snout and sticky tongue of an anteater.
Also, the males have a four-headed penis.
Not kidding. One shaft, four heads. Which is odd, because the female echidna reproductive tract only has two branches. Some of the stuff I've read this morning says that the male echidna mates using only two of his four heads at a time. Then, he'll find another lady echidna and let the other two heads have a turn. Another option, presented by National Geographic: He mates twice with each lady echidna, using first two heads, and then the other two.
National Geographic has helpfully provided visual evidence of this four-headed penis.
I'm putting the photo under a cut. Partly for comic effect, and partly because what is seen can never be unseen.
Read the rest of the National Geographic article on the lives and weird biology of the echidna. (That's the only penis shot. Promise.)