Continuity mistake: When the mouse is serenading the female mouse with his guitar, she throws down a flower at him and there is only one leaf on the stem. But when Speedy Gonzales comes along and takes the flower, there are now three leaves on the stem.
Continuity mistake: When Sylvester is chasing Speedy, Speedy runs into his mouse hole and you can see there is nothing outside of it. But when Sylvester comes back with a gun, we cut to Speedy and there is now a mat outside the hole.
Continuity mistake: When Speedy Gonzales makes Sylvester jump, you can see that Sylvester's chest is shaven, but when he is chasing Speedy in the next shot, his chest is now its usual white.
Continuity mistake: Sylvester puts a large wedge of cheese on the ground to lure Speedy out of his hole. But when Speedy takes the cheese, it has changed to a small, thin slice.
Revealing mistake: When Speedy Gonzales is watching Sylvester drink Tabasco sauce from the tank that sends him miles into the horizon, watch Speedy's tail: it disappears before the scene ends.