I chewed my nails until I got braces, at which point they interfered with my bite. Then I started chewing my lip. *shrug* It sounds more like a way to cope with stress, like thumb sucking or stroking one's belly button. I'm not sure you can guilt a child into stopping the habit, because it's soothing for them. You may need to find some other way for him to soothe himself and then gently remind him of the new method, rather than make a big deal over it. Being two, he'll likely resist any effort to MAKE him stop, in order to assert his will. From experience, I can tell you that even seeing blood occasionally or having too-short nails won't stop a kid - I was shocked occasionally to see I'd nibbled so much, but I couldn't really stop doing it either, until (with braces) I just couldn't get satisfaction from it anymore. Not sure this helps, but I hope you'll get something from it. :)