Biting babies’ cheeks and toes. Have you ever seen grownups interact with babies? Not only do they raise the pitch of their voice to mimic the baby’s, but also often, they will take a playful, gentle peck or two at the baby’s toes or cheeks. This behavior could be due to two phenomena, say scientists. First, the same brain chemical, dopamine, which activates when one smells a baby, is the exact same as when people eat food they enjoy. Secondly, such gentle nips may be a remnant of humans’ evolutionary origins in the animal kingdom. Play-biting is a much-observed phenomena among many species of animals.