Continuity mistake: When the Riffian finds Stan and Oliver in the store cupboard, he stands on some tacks and you can see he drops his knife in the process, but when we see the Riffian a few seconds later, the knife is now back in his hand.
Continuity mistake: When Bosko is sitting in the trench, he spots a piece of cheese on a mousetrap and eats it. In the next shot, the mousetrap has disappeared.
Continuity mistake: When Stan and Oliver are speaking to the ice-cream salesman, the amount on the till reads "05", but after Oliver has given him the money to pay for the ice-cream, the amount is now "10."