Revealing mistake: When Sylvester is on the run from Porky, he dives under the bed, but the cels of him diving were placed over the bed, so that he appears to dive on top of the bed and disappear.
Kitty Kornered (1946)
1 revealing mistake - chronological order
Continuity mistake: When Porky is thrown out of the house, the cat next to him has yellow eyes, but in the next shot they are white.