Hmm, I probably wouldn't freak out but maybe that's because Pie has been known to chomp down in moments of extreme frustration. TBH I don't see it as a learned behaviour, when she does it she's clearly hugely frustrated... I think it's almost more of an instinctive thing IYKWIM? I mean I would hate to hear of her being bitten by another child, but I don't think I'd freak out as such... because I agree with you, I think it's kind of normal. They generally grow out of it very quickly.