I found this out the hard way this afternoon. While talking to my BR hen (who's a little over 2 months old), she tried to bite my tongue! I guess that's what she tried to do, but when she pecked, she actually hit one of my teeth...lol
They are attracted to shiny/light things - teeth and eyeballs are common targets for pecking, so it is important to stay on your toes when you have them in close proximity to your face.