Continuity mistake: When the teachers and doctors are saying to Stan, Kyle and Butters that Eric has AIDS, Kyle holds his hands up and says "hang on." Camera cuts and his hands are at his side. (00:04:15)
Continuity mistake: The way Kyle holds the Xbox 360 changes between shots. In one shot the green circle is in his left hand, but from the side, the green circle is in his right hand. (00:13:20)
Answer: He appears in at least 5 other episodes, but usually just as a background character. He can be seen at Cartman's party in "Immaginationland". He was also one of the kids trying out to replace Butters in the "Professor Chaos" episode.
Bishop73