As a kid I had my nails bitten to the quick.I also chewed my sleeves and twisted my hair I was a sad/nervy kid. I tried all kinds of paint-on bitter-tasting products.None worked. When I was about 12ish? I looked at a guys nails that were just gross/filthy. I had this instant mind picture of biting them (UGH!) and from that day have not bitten my nails. I have very very long thumb nails, I use the right hand one as a guitar pick. It's a real upset when it gets broken off in the garden.( I can't use a plectrum) I have long right hand nails and I try to keep my left hand ones short...gosh they grow quickly.
So maybe try that yertle...a mind picture. Or keep an emery board handy and use that.
I have transformed my ugly feet this summer, almost unbelievable, by regular home pedicure. I just so wanted to wear pretty sandals. I never had any "beauty " routines, but this getting old thing is a bit freaky. I make time now and it does help...thank goodness.
It's not a crime to bite your nails, but if you want to stop, you can try some things...Good Luck.
PS: my sister bounces her leg, CONSTANTLY. Someone told her she'll get Parkinson's disease. Crikes, I hope not. I also chew the inside of my lip...working on that one.**cass reminds herself to sit up straight** old dog trying to learn new tricks...hooooooooooowl.