This slip up is on the 2nd halloween special, it is where both Cartman's are watching Terence and Phillip. On the screen Terence and Phillip are dressed as ghosts and the one on the right (Phillip) farts so then the one on the left (Terence) says 'that fart was ghoulish Terence' when really he was supposed to say 'that fart was ghoulish Phillip' just a minor slip up eh?