Guinea pig

s were small Earth mammals often used by humans for scientific experimentation. Because of this usage, the term "guinea pig" also came to mean any test subject, and not specifically an actual rodent.

When posing as laboratory assistant of Dr Gavin Dexter in a medical research centre in Berkshire, Will Sullivan was tricked into believing that guinea pigs were being used to find a cure for the deadly Marberg virus. However, when he went into the secure treatment facility to inject the animals with the antidote, he discovered that the "guinea pigs" were in fact human test subjects. (BFSJS: Fatal Consequences)