gristi

1. to bite; to gnaw
   Ne boj se, pas ne grize. — Don't worry, the dog doesn't bite.
   Stalno grize nokte kad je nervozan. — He keeps biting his nails when he's nervous.
2. (of conscience, doubts) to gnaw at; to trouble
   Grize me savest što joj nisam javio. — My conscience is nagging at me for not letting her know.
3. (gristi se) to fret; to beat oneself up
   Nemoj da se grizeš zbog toga, nije tvoja krivica. — Don't beat yourself up over it, it's not your fault.
4. (of rust, acid) to corrode; to eat away at
   Rđa polako grize staru ogradu. — Rust is slowly eating away at the old fence.
5. colloq. (of a person) to snap at
   Što me grizeš, nisam ti ništa uradio? — Why are you snapping at me? I didn't do anything to you.

The perfective is ugristi; for dogs and snakes ujedati / ujesti is also common.