Continuity mistake: When Bugs is viewing footage of the previous encounter between Cecil Turtle and himself at the start of the cartoon, you can see that viewed from behind, the projector only has one reel. When we see Bugs eating his carrot in the next shot, there are now two reels.
Continuity mistake: When Jerry emerges from the dollhouse wearing the doll's clothes, you can see the safety pin on Tom's diaper is pointing up, but when see Jerry strolling past him in the next shot, the pin is now lying face down.
Continuity mistake: When Droopy is standing the door, he tells the convict he's going to call the cops. At this point you can see there is nothing next to Droopy on the frame, but in the very next shot a hinge has appeared.