Continuity mistake: Chief is tied to his kennel around the collar. But when Copper cuddles up to him for the first time, the rope tied to his collar disappears for a shot. (00:10:35)
Continuity mistake: When Snoopy is at the library, he picks out a book and you can see there is nothing on the front cover, but when we see a close up of the book in the next shot, the words "How to Perform Magic" have appeared.
Continuity mistake: When Yosemite Sam tells the devil that he has "the very varmint in mind", you can see there are no flames coming up from the pit behind him, but in the next shot flames have suddenly appeared.