Continuity mistake: When Bugs shoots Sam in the face when trying to shoot a can, the can lands in front of Sam. In the next shot, the can has disappeared.
Continuity mistake: When Bugs and Sam start their duel, you can see there is a glass at the end of bar counter. But when Bugs goes to the end of the bar, the glass has disappeared.
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.