During the song "That's All I'm Askin' For!", when the guys are standing in the ling with their arms dancing back in forth, right before it goes to the next shot, you can see Trey Parker (Alferd Packer) mouth the word "cut" to end shooting.
When Alferd Packer is running from the crowd from the bar, there is a clear, visible line in the sand where he is supposed to run.
Matt Stone is correctly credited as "Matthew" in the opening credits, but misspelled as "Mathew" in the closing credits.
When George walks past the Indian woman, his car keys are heard jingling in his pocket as he goes out of the shot.
During the argument about musical keys, Frenchy says "The relative minor is three half tones down from the major, not up!" The scripted line was supposed to be, "The relative minor is three half tones up from the major, not down." Thus establishing his further knowledge (or lack thereof) of music theory.
Right before Packer and the others meet the trappers for the first time, you can clearly see that Leanne is tied up. She is also clearly tied up during the "That's All I'm Asking For!" song. Right after she ran away, Noon asks Packer if she was tied up and Packer replies that he never ties her up.
Frenchy Cabazon states that his song about life as a trapper is in F-sharp major. The song is actually sung in F minor, with the refrain sung in A-flat minor.
Matt Stone's real voice is briefly heard when Humphrey says the lines, "How far to Colorado territory?" and "Watch out for that bear trap."
During the "Trapper Song", in music theory terms E-flat is the relative minor of F-sharp; however, it wouldn't be "spelled" that way. That would be called D-sharp minor.