Gerbiling refers to an unsubstantiated sexual practice in which live animals, such as gerbils, mice, hamsters or rats, are inserted into the human rectum for the purpose of sexual pleasure. Although there have been a few attempts to verify whether gerbiling is a real practice, to date most people believe it's an urban legend as no first-hand accounts have been obtained, nor is there any peer reviewed medical literature describing gerbils as one of the many other foreign objects that are removed from people's rectums in emergency rooms every year.
It is also believed the gerbiling is a homophobic legend designed to denigrate gay men and anal play in general.
Bottom line? It is highly unlikely that anyone has put a gerbil in their ass; the act may even be impossible.
More About Gerbiling
Many people argue that gerbiling is highly unlikely. Most rodents have sharp teeth and claws, which would like cause serious harm (not pleasure!) to delicate rectal tissue. Although people insert many, many unsafe things into their rectums (and end up in the emergency room as a result) most people have chalked gerbiling up to urban legend.
In general, anything inserted into the rectum should be sanitary and sanitizeable, include a wide enough base that it doesn't disappear into the rectum, and should be free of any sharp corners.
