Continuity mistake: When Tom is tying the string on the alarm clock whilst assembling his mousetrap, you can there is a bar which the string is attached to and the wall next to it is perfectly fine, but in the next shot there is a piece broken out of it.
Continuity mistake: When the stick-mouse pulls Jerry up to the drawing board, you can see some string on the bottom left hand corner when he shows Jerry the plan. When Jerry and the stick-mouse stop at the end of the drawing board after seeing the cat, the string has disappeared.
Continuity mistake: When we see first see Jerry's mouse hole, it's in a wooden section of the attic wall to the left of the blueprint. When Tom has finished assembling his mousetrap, the mouse hole is now in a white wall on the other side of the attic.
Continuity mistake: When Tom finishes drawing up the blueprint, he draws a mouse and writes the word "Mouse" underneath it. When the blueprint comes to life after Tom lies down on the bed, the word "Mouse" is now underlined.
Continuity mistake: When Tom finishes drawing up the blueprint, the stand with the pot and cup on changes position between shots.
Continuity mistake: Before Tom is about to draw a line on the alarm clock on the blueprint, you can see on the left hand side of the clock there is an "A" and an arrow, and on the right hand side is some writing. When Tom draws the line, the "A", arrow and writing have all disappeared.