The dumbbell that Larry holds in his left hand disappears in the next shot.
When the boys run into the athletic club, it has twin glass doors. But inside, there's only a single door, and it's made of solid wood.
The left shoe that Moe takes off to tickle Curly's foot reappears again when him and Larry drag him up from the floor.
Obvious stunt doubles for Moe, Larry, and Curly during chase scene near beginning of film.
The mug that Bustoff uses to drink in the restaurant is actually made of paper, thus him being able to easily squash it with his bare hands.
When the Stooges are seen trying to escape after Bustoff is knocked out cold by the dumbbells, the body for him is actually a dummy wearing a black t-shirt and the position of his body changes.
Moe nearly forgets his cue to twist Curly's ears with Larry.
When the Stooges crash into the baby carriage, Curly is visibly having trouble standing up.
The boom mic is visible at the sink in the corner of the dressing room when Larry goes over to Moe and Curly that Tony and his henchman are coming in.