Ouch! Yes, biting hurts. My dd started at 4 months (she's almost 6 months now) and bites usually daily atleast once, and more if she's being extra fussy. It does usually happen when she's distracted or getting bored, had anough of feeding and not wanting anymore. Not sure what you can do to stop it happening but if you say OUCH loudly they do stop and look up at you (....and normally laugh or smile, little monkeys!) x