Cartman Gets an Anal Probe - S1-E2
Revealing mistake: When Stan walks away from Kyle while saying, "I gotta get a piece of loving while the getting's hot," a blue piece of construction paper briefly appears at the bottom right for a second. At the same time, what appears to be a big and a small shadow briefly appear at the top right for a few frames. Then, after Kyle says, "Rats," a human hand suddenly appears on screen for one frame. (00:13:08)