Other mistake: In the beginning the guy cuts a triangle in a banner, but the inside piece is floating.
Continuity mistake: When Puss is telling his childhood story and he is in the orphanage, when Boy Blue spins Humpty, Humpty's hat is off, it comes back later in another shot.
Deliberate mistake: In the opening title sequence, just after the title of the movie is shown, Puss cuts a P with his sabre into a curtain or flag. In the middle of the P, there is cloth remaining, but since he cuts edges all around this to make the Capital P, this cloth should fall away as it is no longer attached to anything, yet it floats in mid air.
Factual error: The "Great Terror" turns out to be a giant goose, but you see in the shot inside the castle that its footprint is not webbed, even though geese have webbed feet.
Continuity mistake: After Puss breaks out of prison he rides the giant Great Terror goose using coloured bunting as reins to steer and control her. In one medium shot the bunting has disappeared, but it magically reappears in the next close-up of Puss sitting astride the goose's neck.