Anyone who has spent much time with babies and toddlers knows that they put everything in their mouths. This includes other children and adults. Biting is sometimes a way of learning about another child. If I bite Andrew, I hear a high pitched scream and my special adults come running to my side. I wonder if it will happen again.
Toddlers are learning to have an impact on their world and biting definitely has an impact.
Modeling or copying the actions of others is an important and powerful way for toddlers to learn. Unfortunately sometimes the toddlers learn negative behaviors like biting. Any adult who has spent much time with a group of toddlers can testify to the fact that biting is more contagious than chicken pox. Toddlers have very limited language skills. Consequently, biting is a way to register a complaint.