Guinea pig

A guinea pig is a mentioned only creature that lived before the Great War.

Background
The animal is frequently used as an idiom for one who is the subject of an experiment. The overseer of Vault 88, Valery Barstow states that the Vault-Tec Handbook urges overseers to refrain from using the words "guinea pig" to describe test subjects, no matter how apt.

Mentions

 * If the Lone Wanderer asks Clover to go into the purifier, she will respond that they need to find another guinea pig.
 * When recording a holotape for his girlfriend Claire, crime boss Eddie Winter, explained experimental treatment he had been receiving in an attempt to lengthen his lifespan, stating that he was their guinea pig.
 * Dr. Penske asks the Sole Survivor to test out a new strain of mutfruit she just developed. They can choose to decline, stating they are not going to be her guinea pig. Dr. Penske will then ask what a guinea pig is.
 * John is a hair stylist, and wants to try out a new look on someone. He asks his mother Cathy if she would be willing to be his guinea pig.
 * Vadim Bobrov is attempting to convince patrons to be a guinea pig, determining alcohol consumption limits.
 * Frederick Rivers reports that for the testing of a new fabricator, Briana Lyon was their first guinea pig, then correcting himself to describe her as their first user.

Appearances
Guinea pigs are mentioned in Fallout 3, Fallout 4 and its add-on Vault-Tec Workshop, and Fallout 76.