to mesh or engage, used of gears or mechanical parts

to gnaw; to bite; to nibble or chew on something persistently

the order of rodents, including animals such as rats, mice, and squirrels

to gnaw; to bite with the teeth like a rodent

rodent; any animal of the order Rodentia

literally meaning a cornered rat will bite a fox; used to describe how a person driven to desperation will put up a fierce fight.