a guinea pig

The phrase "a guinea pig" typically refers to a small mammal native to South America, known for its short legs, round body, and squeaky behavior. It is commonly kept as a pet due to its docile nature. However, the term "guinea pig" is also used metaphorically to describe a person or animal used as a test subject or experimental object in scientific research or experimentation. In this context, a guinea pig is someone or something that is subjected to unknown or potentially harmful substances or procedures to gauge their effects or outcomes.