Continuity mistake: When Tom and the mouse exterminator pry up the entire wall to catch Jerry, the exterminator's feet are positioned sideways, but in the next shot they are facing straight.
Continuity mistake: When the mouse exterminator takes a magnet out of his bag to attract Jerry who has eaten a steel nut, you can see there is nothing coming out of the bag, but when the exterminator has captured Jerry, an axe appears out of nowhere.
Continuity mistake: When Tom picks up a telephone book, you can see he is holding the book with both hands, but when we see a close-up of the "Ajax Mouse Exterminators" in the next shot, his hands are nowhere to be seen.
