South Park Episode 101 - "Cartman Gets an Anal Probe"

As Kyle, Stan, Kenny, and Cartman wait for the school bus, Cartman tells the boys about a dream he had the previous night about being abducted by aliens. The others try to convince him that the events actually happened, but Cartman refuses to believe them. Chef pulls up in his car and asks if the boys saw the spaceship the previous evening, inadvertently confirming Cartman's "dream", and relays stories of alien anal probes (which throughout the episode Cartman denies he experienced). After Chef leaves, the school bus picks up the boys and they watch in horror as the aliens abduct Kyle's little brother, Ike. Kyle spends the rest of the episode attempting to rescue him.

At school, Cartman begins to fart fire and Kyle unsuccessfully tries to convince his teacher Mr. Garrison to excuse him from class in order to find his brother. When Chef learns that Kyle's brother was abducted and sees a machine emerge from Cartman's rear end, he helps the boys escape from school by pulling the fire alarm. Once they are outside, Cartman reiterates that his abduction was just a dream, when suddenly he is hit by a beam and starts singing and dancing. Soon afterward, a spaceship appears. Kyle throws a stone and the spaceship fires back, propelling Kenny into the road where he is run over by a herd of cows and a police car, killing him.

Stan and Kyle meet Wendy at Stark's Pond and she suggests using the machine lodged inside of Cartman to contact the aliens. To lure the aliens back, the children tie Cartman to a tree and then an 80-foot satellite dish emerges from his rear. The alien spaceship arrives and Ike jumps to safety. In the meantime, the aliens communicate with the cows in the area, having found them to be the most intelligent species on the planet. Cartman is again abducted by the aliens and returned to the bus stop the following day.

http://en.wikipedia.org/wiki/Cartman_Gets_an_An...