never seen this happen with nice before..but if the one receiving the 'treatment' wasn't protesting and there isn't any sign of injury, I wouldn't worry about it.

What sort of food are you providing? Do you have males with the females or just strictly a group of females only with no breeding? Describe your setup? (or better yet, provide pictures! Hasn't been enough activity here and fresh pictures will be much enjoyed )
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PHLdyPayne