Continuity mistake: During the slow-motion sequence, Speedy slams the mallet on the cat's paw and leaves the mallet on the ground when he rescues the mouse. When he puts a stick of dynamite on the cat's tongue, the mallet has gone.
Revealing mistake: After the alley cat has put Fernando in his mouth, Speedy runs back and forth before hitting the cat on his foot. If you watch carefully, you can see nothing hits the cat's foot at all, but he reacts as if in pain.
Continuity mistake: During the slow-motion sequence, Speedy approaches the alley cat with a firecracker and you can see that the cat's hair is sticking up, but when Speedy jumps on the cat's outstretched tongue in the next shot, his hair is now flat.
Continuity mistake: After the clock strikes three, the camera pans in on the exit of the mouse hole at the Cantina and you can see there is nothing above the hole. When the mice exit the hole in the next shot, the word "Cantinita" has appeared.
