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Someone or something used as the subject of an experiment. Jane used her husband as a guinea pig to try her new baked chicken recipe. Craig earned a little extra money by signing up to be a guinea pig in some local clinical studies.
a guinea pig
COMMON If someone is used as a guinea pig, new ideas, methods, or medical treatments are tested on them. The new technology should allow us to study genetic disease without having to use humans as guinea pigs. This is the first time I've cooked this dish so you are my guinea pigs.