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 we see the cats lounging around, the bottle the drunken cat is holding has nothing on the label, but in the next shot it now reads "Arsenic and Old Grapes."