Teeth baring:When a dog's lips curl back this shows that the dog has a strong urge to bite.This is an unconscious reflex;designed to get the soft flesh of the lips away from the teeth before the dog bites;and is often misinterpreted as a way of communicating aggressive intent. For example;many dogs will curl their lips back into a "snarl" when they take a cookie or bone.A rare from of teeth baring is seen in the from as a submissive grin.