Guinea pig

He became a human guinea pig and was paid by the company.

[H]e spoke of the unwisdom of volunteering one's services as a guinea pig.

My dad told me about his days in the Navy: He'd agreed to be a guinea pig in exchange for a shorter enlistment. They kept him awake for a week straight.

A good seaman he is... none of your guinea-pigs.

I promise you, to me it was no slight penance to be exposed during the whole voyage to the half sneering, satirical looks of the mates and guinea-pigs.