What do you do when your 4-month-old baby starts to bite your nipples?

I'm not sure if this has scientific explanation (or maybe I'm just lucky, haha) but this is what did. Even before she has no teeth yet, around 2mos old I would always whisper in her ears 'Please don't bite Mama, Mama will get hurt.' I keep doing this until her 1st tooth started to erupt, and yes it looks like she listen to me. She never bite me until now that she has 7 teeth already.