Room and Bird (1951)

Continuity mistake: When Sylvester's owner tells him that she will get into the hotel, you can see that she is wearing a brooch on her shirt. But when she is carrying Sylvester around her neck in the next shot, the brooch has vanished.

Continuity mistake: When Sylvester leaves his room to deliver the note under Tweety's room door, you can see there is nothing on the wall between the two doors, but when Tweety goes over to Sylvester's room, a green square has appeared.

Continuity mistake: When the doorman comes up in the lift and sees Sylvester chasing Tweety, the walls by the lifts are coloured blue, but when the doorman leaves Sylvester's room later on, the walls are now green.