Cute Rat Pose

Rats are often used in scientific experiments; animal rights activists allege that treatment of rats in this context is cruel. The term "lab rat" is used, typically in a self-effacing manner, to describe a person whose job function requires that they spend a majority of their work time engaged in bench-level research (i.e. a scientist or research assistant).
• Rat in terminology
Rats are frequently blamed for damaging food supplies and other goods, or spreading disease. Their reputation has carried into common parlance: in the English language, rat is often an insult. Rat is generally used to signify an unscrupulous character. Writer/Director Preston Sturges created the humorous alias "Ratskywatsky" for a soldier who seduced, impregnated, and abandoned the heroine of his 1944 film, The Miracle of Morgan's Creek. It is a term (noun and verb) in criminal slang for an informant - "to rat on someone" is to betray them by informing the authorities of a crime or misdeed they committed. Describing a person as "rat-like" usually implies he or she is unattractive and suspicious.
Among unions, "rat" is a term for non-union employers or breakers of union contracts, and this is why unions use inflatable rats.