Popcorning behavior is a fun sight—as long as you know what it is. Otherwise, it can scare you. During this action a pig runs around very fast and suddenly leaps straight up in the air, twitching and squeaking. It then lands and takes off again, often in another direction. This activity shows pure joy. Babies start to popcorn when they are about two weeks old or so—they may try it earlier, but they usually fall down instead.