guinea pig

(noun) a person who is subjected to experimental or other observational procedures; someone who is an object of investigation. Synonyms: subject, case, guinea pig. Examples: "The subjects for this investigation were selected randomly." "The cases that we studied were drawn from two different communities."

(noun) stout-bodied nearly tailless domesticated cavy; often kept as a pet and widely used in research. Synonyms: guinea pig, Cavia cobaya.