During the La Resistance towards the climax of the song when the soldiers can be seen singing "Tomorrow night!" on a four-way split screen, the lip-sync doesn't match for the first "Tomorrow night!" and on the third one the mouths don't open at all.
In the song "It's Easy, Mmmkay", Mr. Mackey tells the children "With bitch drop the t 'cause 'bich' is Latin for generosity". Actually, there's no such word as 'bich' in the Latin language (the most common translation of generosity is 'magnanimitas').
Sheila states that she is placing Terrance and Philip under a citizens arrest, but then produces a court order for their arrest. A court order indicates government authorization of such an action, making it not a citizens arrest.
During the video from the Whitehouse, the President is talking about the horrific bombing of the Baldwins at 5am that morning. The scene a few seconds earlier depicts Canada bombing the Baldwins. They are by the pool talking on the phone and it is day outside. There would be no way that the bombing happened at 5 in the morning, before daylight.
The night of the La Resistance meeting, before Kenny appears as a ghost, Cartman can be seen loading a mirror and a rope into his backpack. These are items that The Mole requested they bring for the rescue operation. Only at this point in the movie, they hadn't met The Mole yet.
When Kenny is brought into the hospital, there is a schedule on the wall next to the door (Dr. No is scheduled to 'Kill Bond'). When Kyle is worried that their mothers will find out that they went to the movie, the Doctor column has vanished from the chart. A little later, the columns are reversed.
When the switch is thrown to electrocute Terrence and Phillip, it's pulled downwards. A few shots later, we see Cartman jump in to save T and P by turning the switch off. He also pulls the switch downwards instead of upwards.
When the boys are greeted by Chef when getting their lunch, the word "Chef" on his apron appears with only the first letter capitalized. In the next shot, the word "Chef" on his apron appears in all caps.
In the first shot of the movie (with the mountain, birds and Stan's house), when Stan opens the door and starts singing, he begins walking down the steps, but then, when it zooms in, he's back on top of the steps, then walks down them again (this goof only appears in the international DVD release).
When Cartman is coming to end of singing "Kyle's Mom's a bitch", Kyle's mom appears behind him. She starts with her hands down by her sides, then in the next frame we see her she has her hands on her waist, in the very next shot she has her hands down by her sides again.
The graph of Canada's economy shown early in the film reveals that a significant portion of the country's income comes from filming of The X-Files. In actual fact, The X Files has not been filmed in Canada since early 1998, well over a year before the film was released.
Sheila reveals her hatred on Canadians by remarking about their flapping heads and beady eyes on the news and declaring war on Canada yet as Kyle points out near the end of the film her adopted son Ike is from Canada meaning she had no room to hate Canadians.
Mr. Garrison pulls down a lever to electrocute Terrance and Phillip in the Electric Chair.(note - down = Lever on). When Cartman goes to stop Terrance and Phillip from being electrocuted, the lever is up which means the electric chair should be off, but instead on.
In the scene were the children of '' La Resitance '' talk about its plan to rescue Philipp and Terrence a huge sign saying '' Viva la Resistance '' is seen. It's obviously a reference to the French's Resitance in WWII. The correct french would be '' Vive la Résistance ''. However, seeing as they are elementary school students, it can be considered normal that it is not spelled correctly.
The boys were told they needed to be with an adult to see the Asses of Fire but strangely enough the other kids except Wendy and Gregory somehow manage to see the movie and they all watch the movie a second time without adults.