It may seem pretty obvious what they're for (what, with their relentless one-mind track), but there are still many mysteries surrounding these anatomical masterpieces. For instance, how come lots of species sport a bone in theirs while humans (and a few other mammalian species) do not? How come felines have barbed phalluses and ducks have... well, you can check out that weirdness for yourself.
But even if we stick with boring human subjects, how exactly do they work? How is erection achieved? Is it merely an inflatable tube? If so, why can't it bend? How come it's so hard? And how exactly does it stay erect?
If you've ever wondered about any of these questions, it seems that Diane Kelly can answer at least a few of them in the following TEDTalk presentation:
I think I'm going to go play with mine for a while, all in the name of science, of course :)