
Continuity mistake: When Gary is remembering at the start of the film the incident with his family and is looking at the picture in the mirror, you can see there are 4 people in it. The next shot when Gary is speaking with Spottswoode the picture (to the left) has changed to being just 2 people in the picture.
Answer: I read an interview with Trey Parker and Matt Stone where they said that they had not intended for it to be that way but that when they made the Matt Damon puppet, it looked so retarded that they thought it would be funny to just have him be retarded in the movie and only say his name. They said it was nothing personal against Matt Damon.