During the later seasons, Matt Stone started using auto-tune when voicing Kyle to make him sound more like a little kid.
That fart was absolutely GHOULISH Terrance.
Exactly who is related to whom in the Marsh family is never consistent. Early episodes imply that Jimbo and Marvin (Stan's grandfather) are on Sharon's side of the family, whereas more recent ones imply they are on Randy's side. Being on Sharon's side makes sense for Jimbo, as he has a different last name. However, Marvin's last name is, indeed, confirmed to be Marsh. Matt Stone revealed in an interview that Jimbo Kerns is Randy's half-brother.
The Braniff sign at the end of the credits was used for fun in the first episode. Braniff is originally an airline. Trey and Matt got permission to use the sign for every episode.
There is a persistent rumor that, in the "Big Gay Al" episode, the line "And these South Park Cows are being absolutely molested by Middle Park. I haven't seen so many children since..." was initially followed by "since Michael Jackson came to town". This rumor is entirely unfounded; numerous tapes made of the episode as broadcast prove this, and nobody has yet to offer any actual evidence to the contrary other than memory. Despite this, the rumor persists.