Guinea pig
From Memory Alpha, the free Star Trek reference.
The Guinea pig was a small pet animal native to Earth. It was frequently used as a test subject in scientific research.
In 2371, the all-Klingon B'Elanna Torres told Sulan that Klingons found honor as warriors on the battlefield, not as guinea pigs in a laboratory. (VOY: "Faces")
In 2373, Captain Janeway remarked to The Doctor she'd be his guinea pig for testing his antigen against the macrovirus. (VOY: "Macrocosm")
In 2374, after Harry Kim and Tom Paris had been copied by the Silver Blood, the mimetic Kim remarked he'd go down to the surface of their planet and let mimetic Tom play guinea pig for the Doctor. (VOY: "Demon")
