Continuity mistake: In the beginning, the black sheep falls backward into the fence, and the other sheep laugh. Then the angle changes, and he's about three feet from the fence. He didn't move, and he's still in the same sitting position he was in before.
Factual error: When Wilbur and the others are going to save that black sheep from the fox, you see some pawprints on the ground, supposedly from the fox. Fox prints are smaller, and should have claw marks.