Humans give flowers and candy when wooing a lady. Penguins give rocks. Not just any rocks, though -- male gentoo penguins search through piles of pebbles to find the smoothest, most perfect ones. When a penguin has selected his pebble, he presents it to his intended companion. If she approves, she puts the stone in her nest and the two are well on their way to becoming mommy and daddy birds. Pebbles are so important to the penguins that males often fight over the prettiest selections.