K.B.
I found my daughter was doing that and when I asked her about it she said "they bug me." It was because her nails were jagged and I hadn't really shown her what to do with her nails to keep them maintianed. Doh! I taught her to brush her teeth, wash her hair and all of the other things but didn't think to show her how to file her nails.
I got her a cute pink nail file at Beauty Warehouse and some lotion and showed her what to do when her nails start "bugging her." I try to get her to file once a week or so. I think some people's nails may be more brittle and prone to hangnails. Who knows, it might help!