Goofs

When Margaret cries about Dennis being lost, she holds the doll that was stolen from her earlier and which she has somehow reacquired before the thief's apprehension.

When Dennis is taking a bath, the water is low to Dennis' waist, but in the next few shots, it's high almost up to his chest.

The door lock on Dennis's side of the station wagon changes positions.

When Dennis is in the bathroom squirting out the nasal spray, the toothpaste on his chin vanishes and then comes back again

The architecture of the inside and outside of the Wilson's home doesn't match.

In all of the Dennis the Menace stories, both Henry and Alice (his parents) calls both Mr. and Wrs. Wilson by their first names "George" and "Martha." However, while Henry calls Mr. Wilson "George" once when he first interacts with him, like the way it is in all the other stories, he somehow ends up calling him "Mr. Wilson" twice instead of "George" during their chat.

When Mr. Wilson investigates the vacuum cleaner, you can see the wire that is used to control the hose.

When Switchblade Sam takes an apple away from Gunther with his switchblade, the hand is obviously a fake plastic hand rather than the little boy's, as it wobbles when the switchblade makes contact with the apple.

Switchblade Sam's (Christopher Lloyd) hair is obviously hair extensions. This is especially obvious when he is looking up at the tree house when Dennis and his friends are in it hammering nails. You can see a white line on his head of where they are attached.

When Dennis is in the Wilsons' bathroom, the toothpaste on his chin is clearly fake.

After when Switchblade Sam walked into Mr Wilson's house, and stole Mr Wilson's gold, you can see Sam running out of the screen door and the main door is wide open.

When Mr. Wilson flinches from the tack taped to the doorbell button of Dennis' house, the button is not pressed enough to let it ring, but you hear the ringing.

After Dennis shoots a marble at Switchblade Sam's head, his mouth doesn't move when he says he knows how to make the campfire bigger.

When George Wilson goes to look for Dennis in his car, the cameras and crew are reflected in the car.

Shortly after George places the lid on the barbecue, the paint catches on fire, even if he didn't notice straight away, he would have had to at some point. And how does the chicken stay intact? Surely it should have been charred.

Switchblade Sam could not have opened Mr. Wilson's safe since he did not know the combination.

When Dennis and his mom are driving to Margaret's house Mason Gamble looks directly at the camera twice.

When Henry Mitchell is leaving for work and talking to Mr. Wilson he unlocks the door but seconds later he holds onto the window frame of an unrolled window. Why lock the door if you leave the window down and why not just reach in and pull the lock up instead of using a key.