What happens if you bit your fingers to your nub?
The correct expression is "bite your fingernails to the nub" or
"bite your fingernails to the quick". You cannot bite your fingers
to the nub---impossible. If you bite your fingernails to the nub,
nub refers to the way your finger ends would look without a nail
sticking out. Nails bitten so badly could bleed and cause the end
of the fingers to be sore.