Guinea pigs were small Earth mammals often used by humans for scientific experimentation and as pets[source needed]. Because of the former, the term "guinea pig" also came to mean any test subject and not specifically an actual member of the species. (TV: The Ark, The Happiness Patrol, The Crimson Horror)
He's doing experiments. That's why we're here. He needs guinea pigs. Guinea pigs like you and me.
When posing as the 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 these animals with the antidote, he discovered that the "guinea pigs" were in fact human test subjects. (AUDIO: Fatal Consequences)