Informing on someone or betraying them, especially to authorities; being a tattletale or informer. Originally referred to hunting rats with dogs.
From rat + -ing. The betrayal sense developed from the negative associations with rats as disease-carriers and pests, combined with the idea of 'squealing.' The shift from literal rat-hunting to metaphorical betrayal occurred in early 20th century slang.
The evolution from 'catching rats' to 'being a rat' shows how animal metaphors shape our moral language. Rats went from being the hunted pest to symbolizing the hunter who betrays their own kind - a linguistic flip that reveals our complex relationship with these intelligent but unwanted creatures.
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