I've been bitten many times (ouch!) and had always read to say "no" firmly, then take baby off the breast. But today I heard something new and thought I'd share it, although I haven't tried it myself- he hasn't bitten me again yet.
A guru in LLL said when they bite, you immediately (but gently) push the baby's face toward your breast. This will cause them to open their mouth, thus releasing the painful grip on your nip, and also startles them a bit. She swears by it. Who knows? Maybe it will work for someone.
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Re: PSA if your BF baby bites while nursing
I've also heard that nursing strikes can be started because the baby is afraid you're going to scream (if you have before when bitten).