My son, who's 3.5yo, was always interested in biting them instead of clipping them, but recently, he's taken them down to the wick. While his fingers aren't bloody, it looks darn well close enough.
I bite my nails, not down to the nubbins, but there's still some white and I prefer shorter nails due to all the typing i do in the day. I'll admit that it's one of my least favorite things about myself and I wish I didn't do it. I cringe looking at other people's chewed-up fingers and feel bad for them too, nothing says repressed anxiety like nail-biting.
Admittedly, we did just move across the county 2.5 months ago and potty training is pretty much done. I thought he was taking it well. Maybe not. As a SAHM I do try to keep him busy but I can't do anything but remind him for the Nth time to stop doing it when he's in his car seat while I'm driving.