Continuity mistake: Even though the moon plays a leading role in the movie its phases get mixed up in a big way: Before Will has his first night out as a semi-wolf there's a shot of a half moon. That's not only just a few days after the full moon when he was bitten, but it's waxing to boot. In the next night, after Will calls Laura, apologizes for his vanishing, and asks her out for dinner there is another shot of a slightly fuller moon, but now it's waning. However, two days later near the end, when Will is locked up in the barn, the moon is full again.
Revealing mistake: Whenever Will does one of his fancy jumps (which make him actually appear more like a monkey than a wolf) you can easily tell that he gets pulled up by a rope because always accelerates on the way up. If he were jumping his maximum speed would be at the moment when he takes off. The softened landings enhance the unrealistic impression.