First Aired: March 8, 2009
Plot: While on his way to buy groceries, Peter instead buys a brain-damaged horse, which not only creeps everyone out but also causes $100,000 worth of damage when Peter enters it in a race and it goes on a rampage. Though the horse ends up dying of a fatal heart attack and Peter disposes of the body by flinging it into Mort Goldman's pharmacy, the Griffins are in debt for initial damages. To make money, Peter works as a test subject for medical experiments, being injected with various genes to see their effects; these include the squirrel gene, the Seth Rogen gene, and the gay gene amongst others.
Lois is initially upset that Peter is now gay, but she warms up to the change when he begins exhibiting stereotypical gay behaviors like shopping for clothes and cooking muffins, only to reconsider her stance when Peter rejects her sexual advances. Upon learning that the effects of the gay gene may be permanent, she decides to make the best of things when Peter suddenly leaves her for a gay man named Scott. Seeing Lois heartbroken and depressed, Stewie and Brian (who is reluctant due to his support of gay rights) attempt to bring Peter back to his normal self by kidnapping him and sending him to a "straight camp" for conversion therapy.
When Scott comes over looking for Peter, Brian admits his actions. Lois states that she is willing to accept Peter the way he is now and takes him out of the straight camp, telling him to go back to Scott. However, the effects of the experimental gay gene are revealed to be temporary and the effects wear off right when Peter is in the middle of a gay orgy with Scott and nine other men. Peter returns to Lois, and they decide to never speak of the incident again. Just when they assume things will go back to normal, Mort flings the body of Peter's dead horse through the wall of the house. After it lands on their kitchen table, Mort can be heard screaming "Take back your fucking horse!".