Video: Two penguins at the Monterey Bay Aquarium decided to make baby penguins in front of their viewing window. In the process, they showed off a fascinating aspect of bird reproductive biology.
Birds use internal fertilization -- their shelled eggs make it a requirement, since ova have to get fertilised before the shell is laid down. But most birds don't have a penis. Instead, they perform what's called a "cloacal kiss": the female opens up her cloaca, the male pushes his out, and they wipe them together as he ejaculates.
Sometimes, as you'll see, the process is a little messy.