Other mistake: As the brown truck drives away in the scene after the man working in the newspaper office is "harpooned" by a Critter, if you look closely as the truck turns a corner you can see some Critters rolling after it. Well, after they roll past the truck in the bottom left of the screen you can see the Critters roll right smack into another parked car. Obviously the crew forgot to add a turning feature to their Critter balls (which were just some fur taped to a basket ball).
Revealing mistake: When the kid who breaks the egg throws it out the window, the egg hits another egg which starts rolling down. You can see the tracks on the grass making it easier for the egg to roll. (00:30:05)
Continuity mistake: When Brad gets to his grandma's house he is standing outside her window. He holds his bag in his left hand and switches it to his right. When it cuts, he switches again. (00:10:00)
Continuity mistake: At the end when Brad kisses Brenda he turns around and walks away. When it cuts, he does the same thing again. (01:17:30)
Plot hole: When the old women are painting the eggs, you can see them blowing the yolk out of some. Why didn't they blow the yolk out of the Critter eggs?
Visible crew/equipment: When the Critters are in the restaurant, The Hungry Heffer, as the camera pans across some Critters eating lettuce and other food. If you look closely, you can see one of the puppeteers hands coming out of the bottom of a critter puppet. The puppeteer is wearing a dark shirt with what look like gloves.
Revealing mistake: When a ball of about four Critters is rolling, after coming out of the antique shop, you can see the wires that are pulling it.
Factual error: For most of the movie you can see mountains and large hills in the background. The movie takes place in Kansas and almost all of Kansas is flat.
Other mistake: When Cindy's dad steps off the freshly hatched critter he lifts his foot to find a bunch of gooey green slime. Where's the fur, eyes, teeth and internal organs?
Revealing mistake: When the bounty hunters are landing the ship, look closely, you can see the wires holding it up. (00:36:30)
Revealing mistake: Nearing the end of the film when the giant critter ball is roll back to town and the good guys are following in the truck, you can see the shadow of the truck in front of the critter ball pulling it along. It's visible in more than one shot.
Visible crew/equipment: Toward the end of the film when the critter ball enters town and the truck swerves to the left of the ball, you can see the feet of a crew member running behind the ball, pushing it along the street.