When Michael tries to pull Eric and his wheelchair into the van while being chased, Michael wears sunglasses when his head is sticking out the van window, but not in the van.
The Mercury Cougar totaled during the car crash scene later drives by, undamaged, during one of the chase scenes.
When Debbie puts MAC (in a teddy suit) into the back of the car, the window changes from halfway up to fully rolled up.
MAC is fully enclosed in the bear suit when he and Eric hit wall after fleeing McDonald's. In the next shot, MAC is suddenly half-dressed, with his upper body visible. Then Eric peels away the empty suit and tosses it aside without taking it off MAC.
When the agents are chasing Eric. 5 agents are chasing him but in the next scene when Eric is rolling down the street 3 agents are chasing Eric. When they chase him in Sears, 5 agents are chasing him but in the next scene 4 agents are chasing him and then in the next scene 3 agents are chasing him.
When MAC is tap dancing on the counter with the McDonald's crew members behind him, there menu above their heads lists items, but not prices.
Old canister-style vacuums do not have a "reversible" motor. Users simply move the hose from one end to the other.
Eric comes up with the scheme to capture MAC with the vacuum cleaner. Though he has no prior knowledge that MAC can be sucked in, he was simply carrying out a childish plan. Whether it worked or not remained to be seen.
When Eric leaves Sears with his mother behind him, the door handles on the store across the street clearly say Sears. The sequence was shot at the Costa Mesa CA store, with a separate merchandise pickup building across the street from the main store.
The same scene of A Snorking We Will Go/Now You Seahorse, Now You Don't (1984) is always playing on TV. This could be a quirk of MAC's odd power.
When the vacuum pulls Debbie across the ceiling and wall, the girl is an obvious dummy.
When MAC is stretched while holding the chain link fence, then shot into the air, strings are visible holding the puppet.
Michael's older, stronger, much larger stunt double pulls Eric and his wheelchair into the moving van.
Obvious dummy for Eric falling off the cliff.
The close-up version of MAC is less than 2 feet tall. The walking stand-in is almost 4 feet tall.
When Debbie sucks MAC into the vacuum and gets flung around the room, a track running up the wall, across the ceiling, down the other wall, and across the floor is visible for the entire scene.
MAC "flies" out of the McDonald's when he sees the agents coming for him. People are clearly holding him up by his arms.
Near the start of the movie, a cameraman reflected in glass screen at the Army lab.
When Eric rolls down the street in his wheelchair to escape the agents, it's clearly his older, taller, skinnier stunt double.