Continuity mistake: When Sylvester and the orange cat take Tweety Pie's nest, you can see the outside of the nest is covered in snow. But when the two cats reach the bottom of the pole, the snow has gone.
Continuity mistake: When Elmer realises there are no more bullets in his gun, you can see there is a tree behind Bugs. But when we see Bugs in the next shot, the tree has disappeared.
Continuity mistake: When the young man says "What's cooking?" to St. Peter at the beginning of the short, St. Peter is holding a feather in his right hand. In the next shot, the feather has disappeared.