If you’re visiting for the first time, this is part 3 of a series. See links to prior posts in this series at the bottom of this post.
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 or is generally used to signify an unscrupulous character; it is also used to mean an individual who works as a police informant. 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.
They're typically associated with filth, bad smell, and have be blamed for transmitting diseases. This gave rise to a number of expressions, including “to smell a rat” and the associated meaning of rat (“a person regarded as despicable”).
Similar to the wonderful variety of appearances of chicken figures of speech in the English language, here is a collection of rat figures of speech from weblearneng.com
1. rat (noun) =
(a) a worthless, disloyal, dangerous man
(b) in labour unions a term used for non-union employers or breakers of union contracts
2. “Rats!” (interjection) = an expression used for some interjections which are considered vulgar, and also to mean ‘Nonsense!’
3. to rat (verb) = to break a promise; to be disloyal
4. to rat on someone = to betray; to cheat someone
5. to smell a rat = to guess that something wrong is happening or to suspect some hidden danger or disadvantage.
The rat series
Rats #9: Good riddance at The Eggplant