They are such nibblers at this age, in spite of all the money we spend on appropriate chew toys!
When Sophie even puts her teeth on me (even without closing down in a bite), I say "Ouch!" in a loud voice, withdraw my hand, and get up and stop playing with her. I sit back down in a few minutes and we try it again. It definitely seems to be helping. Teaching her "drop it" has also helped sooo much in preventing her from nibbling on me when we play together with her toys.