Continuity mistake: When Sam is counting to five when riding his horse, he runs into a telegraph pole and loses his guns in the process. But when he catches up with Bugs on the train, he is holding his guns again.
Continuity mistake: When Witch Hazel is chasing Bugs Bunny up the castle tower, Bugs throws a stone through the window before Hazel appears from behind the curtains. When we see Bugs dressed up as Romeo, the glass panes have disappeared, and when we see Hazel dressed up as Juliet, they are back again.
Continuity mistake: Daffy takes down a gun from the mantle, but when Daffy points it at Bugs in the next shot, you can still see the gun on the mantle.