When Joan Severance's Eve is shown in the shower, the actress / body double has pink bikini bottoms on. These are 'not' on when she emerges in the next shot to remove something from the bag Dave holds up for her.
Wally's ice cream cone changes size in the first sequence.
When Dave falls off the car that rolls down the hill by the Sutherland estate, the stuntman who did the fall lands with his right leg bent and his left leg straight, but when the camera cuts to Gene Wilder on the ground, his left leg is bent and his right leg is straight.
When David sees the carry-on bag through the mirror, the smaller pouch is visible in the reflection. But from the angle inside the bathroom looking out, the bag is clearly turned too far around for him to have seen the small pouch.
When Braddock closes his car door in one sequence, he clearly shuts it on his jacket, yet in the next shot his jacket is free of the door.
When Dave and Wally attempt to check into the hotel posing as the international doctors, the desk clerk didn't check ID which all hotels do.
When Wally and Dave are about to break into the house of 1000 windows, Dave is carrying a big log and as he swings it around, Wally moves his head as if afraid to get hit by it. Wally is blind, so he wouldn't have seen it.
When Dave (the seeing but deaf one) and Wally (the blind but hearing one) are escaping from police custody, they try a locked door and Dave steps away to look around. With his back turned to Wally, Wally frantically yells for Dave by name, and Dave reacts by turning around and going back to Wally and reassuring Wally that he (Dave) is right there.
Dave responds to much of Wally's and other people's conversations throughout the
film without looking at his lips. For Dave being deaf, this would be impossible. Examples are when Dave are looking into the binoculars and at the hotel front desk looking down at his sign-in sheet.
Wally's trousers get wet while pushing the police car into the mud/swamp, and the outline of the knee-high (probably waterproof) boots he is wearing is visible.
When Sutherland turns off the light, Wally ducks before any shot is fired. Later, he asks what happened.
Obvious stunt double for Gene Wilder when he rolls off the car.
Camera dolly tracks when the killers catch Dave and Wally after they escape from the police station.
When Wally stops the police car after driving into the sides of beef at the meat market, you can clearly see that it is Wally's stunt double driving through the driver side window.
When they avoid detection in the motel when police searches it, it appears they escaped through the back window, which would have been impossible if the police surrounded it as they state they did.
The hotel receptionist is credited as "Mitzie", but her tag clearly says "Cindy"
When Wally introduces his friends in the bar, he refers to the female character as 'Lisa'. She then quickly corrects him by saying 'Leslie' which is her character's name.