Peter has a vestigial twin growing of his neck, and he has surgery to remove it and have it become a separate entity.
Did You Know?
The actor Andy Garcia actually was born as a conjoined twin. His twin was no bigger than a tennis ball and was surgically removed. All that remains is a scar on his shoulder. See more
Sorry... the game that teaches you to be a dick.
References The Dr. Oz Show
I Hate Myself For Loving You
Performed by Joan Jett See more