Deliberate "mistake": When Commander Taggert (Tim Allen) and Lt. Madison (Sigourney Weaver) first see the hallway with the chompers, she says, "Oh, screw that!" but if you watch her lips she clearly uses the 'f' word instead of 'screw'.

Deliberate "mistake": When Commander Taggert (Tim Allen) and Lt. Madison (Sigourney Weaver) are about to press the blue button to stop the ship exploding, Lt. Madison's tunic is mostly zipped up. A few seconds later it is suddenly mostly unzipped. Those of you who have access to the DVD of the film can see that there was a deleted scene which was originally intended to go in here.

Factual error: Laredo drives the ship out of the starship docking station and scrapes the main hull on the walls. This would not be possible without either scraping the wings first, as they are much wider than the main ship, or turning nearly sideways, which they clearly don't.

Audio problem: In the beginning scene at the Galaxy Quest convention the crowd is clapping and shouting to see the actors but when they cut to the back of the audience you clearly see the audience are not clapping and shouting, or even moving yet, but the sound of the clapping and the shouting is still there.

Audio problem: When Mathesar says "We need to separate or we'll die," his mouth doesn't move for "We need to separate."

Visible crew/equipment: When the crew is escaping with the beryllium sphere, there a shot where you can see the filming crew at the top left corner of the image.

Continuity: When Guy is introducing the actors at the start of the movie, while he is saying Jason's name, to the right of the screen you can see that Guy is holding a glass of water with a lemon in it. The camera then cuts to an overhead shot of the whole crowd and Guy can be seen clapping with nothing in his hands.

Continuity: After destroying Sarris' ship with mines, we see Guy Fleegman standing to the left by himself as the "aliens" come off the elevator to congratulate them. In the next scene, he is now standing between Alexander and Gwen.

Continuity: When Jason gets in the limo with the Thermians, the limo starts off having no license plate and changes to a California plate between shots.

Audio problem: In the early backstage scenes from the convention, the other actors are angry at Tim Allen's character.  The actor who plays Laredo clearly says "You are so full of sh*t", but it is edited to "full of it."  Those two word edits ('s' word and 'f' word) were done to keep the PG rating, but the editing is sloppy. [This theory could also be expanded to the drug reference mentioned above].

Revealing: When Saris is torturing the Thermian commander, he stops and approaches Commander Taggart; while Saris is talking to Taggart you can see the lips and teeth of actor Robin Sachs behind the mask.

Audio problem: When the aliens are talking to Taggart at his house, in a shot from behind the aliens looking at Taggart in the doorway, the audio is out of sync with the alien leader's mouth. You can see this when he says the word "destruction."

Audio problem: When Jason is at home watching TV after his outburst at the convention, he is flipping through TV channels and finds a repeat of Galaxy Quest. However, he reacts to seeing the show on the TV while we still hear the audio of a previous channel.

Audio problem: When Brandon's parent's are listening to the news reporter talk about the crew not showing up to the convention, his words don't match his mouth at the end of the shot.

Continuity: In the ending scene where the crew is bowing to the fans, Sigourney's character is shown moving her right leg back a small bit.  However, when they show them standing up from the bow, her right leg is fully crossed behind her.

Continuity: When they are rolling the beryllium sphere back to the ship, Fred has his paper bag in his mouth in some shots and it disappears completely in others.

Audio problem: After Sarris' first missile has hit the ship, Jason runs towards Tommy and shouts, "Tommy, let's go, get us outta here, go go go go go." However, what we hear is not in sync with Jason's mouth until the last 'go'.

Audio problem: When Gwen uses her Gilligan's Island analogy, Mathesar says, "Those poor people," and then Tommy says, "Oh brother." We are then shown Guy standing next to Gwen, and Guy says "We're screwed," although if you watch his mouth he actually says something like, "We're dead." This dub is probably for a similar reason to that of why Gwen and Tommy's swearing was dubbed over.

Continuity: When the 4 "nerds" first approach the captain to talk about their supposed problem the girl is standing in a different place than when they cut back. In a later scene the girl is in this position and I believe they reshot the earlier scene while they were doing the later scene.

Audio problem: In the scene where they are rolling the beryllium sphere Laredo is seen helping roll the sphere into the ship and is heard yelling but his mouth isn't moving.