Flicking, hair pulling, etc. can sometimes cause strikes. I know of at least one mom who never got her lo back to the breast after that. When they are really little, teaching them it's okay to bite a washcloth or teether, but not mommy is a good first step, as is putting them down for a while. Then, in a half hour when they decide they are still hungry, you can try it again. Most babies aren't persistent biters (they just try it a few times), but even with a persistent biter there are things you can try such as watching for biting "cues" or stopping sessions when they start to get wiggly.