lab rat

poor as a rat

Synonym of poor as a church mouse.

rat run

A small, usually minor road used by a significant amount of traffic as a short cut or to avoid congestion on more major routes.

smell a rat

To sense something suspicious.

winter rat

An old, unattractive automobile, purchased for little money, to be driven during brutal Great Lakes winters while the owner's "good" car remains garaged and protected from corrosive road salt for the season.