the.com/guinea pig

means A small, plump, tailless rodent kept as a pet, or by extension, a person or thing used as the subject of an experiment or test.

from A double misnomer that has baffled people for centuries. The animal is native to the Andes of South America, not Guinea in Africa, and it's a rodent, not a pig — though its squeals and stout body invited the comparison. One theory holds that 'Guinea' is a muddle for Guiana or simply meant 'far-off and foreign,' the way 'Guinea' got slapped onto many exotic imports; another guesses it nods to Guinea ships that ferried the creatures to Europe, or even to the gold guinea coin one might pay for one. The honest truth is that nobody is certain how the name stuck. The experimental sense — a test subject — came later, in the late 19th and early 20th centuries, when these docile, easily kept animals became laboratory favorites.