Slither

Wincest. Sam is transformed into a Naga-half man, half snake-by a vengeful he-witch. Dean's freaked out. Ruby's a smartass. Castiel's no help. Bobby's got a U-Haul. In case, you know, Sam needs to go anywhere. As they desperately try to turn Sam back, the answer may lie in a shocking secret Sam has kept well hidden for over five years.