Continuity mistake: When Grandma shows her bag with the mice inside to Bruno's mom, her grip on the bag changes between shots: sometimes she is grabbing the upper handle where the yellow threads are; others, the wooden part slightly below the threads; and yet in other shots she is grabbing the lower wooden part. This changes back and forth. Her right thumb also appears and disappears randomly.
Continuity mistake: When the first witch turns into a mouse, the way her empty dress lies on the table changes between the first and second shot, in a mere frame. Check the plate on the left, for example: it swaps from uncovered to covered by the dress. Also, the first shot shows more lace by the edge of the table, while the second shot shows much more silky fabric.