Continuity mistake: When the cat is baking the turkey on the vent, you can see a handle by the turkey. When the cat grabs the turkey, the handle has disappeared.
Continuity mistake: When Sylvester is at the medicine cabinet, he takes out a bottle of Seasick Remedy and starts drinking it. But when we see Tweety in the cabinet in the next shot, the Seasick Remedy bottle is still on the shelf when it should be in Sylvester's hand.
Continuity mistake: When Bugs is making Francois look like a rabbit, he cuts up Francois' moustache to make whiskers. When Bugs says "You make a swell rabbit, Doc!" the whiskers disappear.