Visible crew/equipment: At the beginning of the movie, they show the aliens in their spaceship. Mac is suspended in a hover-bed, but you can clearly see the black wires holding him up.
Visible crew/equipment: In the scene where the car gets stuck in the giant donut, the thick black steel bars holding the car in the air can be seen in the back.
Revealing mistake: In the scene when the aliens first enter Valerie's house, Mac and Zeebo find the fish tank and eat one fish each. The shot turns to Valerie's stunned reaction then back to the aliens, who are smiling widely, pleased with their stunt. If you look at Mac's teeth, you can see they are bright white up to his first molar, which is a give-away at his fake white fronts.