Up until Molly was 11 month old she had three teeth in the bottom of her mouth. About two weeks ago she cut four top teeth all at once. Needless to say she has been a little crabby and is no longer sleeping well. The biggest difference is that she has been biting things. She bites me. She bites toys. She loves to bite Marlins nerf football. If I don't keep it out of her reach, I find her chewing away on a piece of nerf...yuck!