A rodent with a long tail, often considered a pest; to inform on someone as a betrayer.
From Old English ræt, possibly from Proto-Germanic *rattaz. The meaning of 'informer' developed from rats being seen as sneaky, unwanted creatures that infiltrate spaces. This metaphorical extension reflects cultural associations with treachery and betrayal.
The transformation of 'rat' from simple rodent to slang for betrayer shows how animal characteristics become moral metaphors in human language. Rats' survival skills - adaptability, intelligence, and resourcefulness - are exactly what make them successful, yet these same traits become negative when applied to human social behavior.
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