Was Michelle the original wolf that bit Jack? (SPOILERS!)

Really simple: NO! Why? Horses freak out in Jacks (Wolf) presence. If she were the "original" wolf her horse would have lost it as well.

This theory seems to spring from two misconceptions about the werewolves in this film. Firstly, that a person has to be bitten to become a werewolf, when the film clearly explains that this isn't the case. Secondly, that these werewolves can change back and forth from "full wolf" to "full human". Will's conversation with the professor implies that he'll become more wolf-like every night until the next full moon and then become a wolf for good, and the film seems to bear this out.

Besides that, there's no evidence in the film to support the idea of Laura having been a werewolf all along. She displays no wolf-like characteristics until the last scene, animals aren't afraid of her, and there are several scenes where she's freaking out over the very idea of werewolves, which would be odd if she were one herself.

The real nail in the coffin for this idea, of course, is the climactic scene in the stable. If Laura is a werewolf, then why doesn't she change when Will and Stewart do? Why is she running away from Stewart and feebly trying to fend him off with fire extinguishers and pitchforks, when she could just "wolf out" and fight him lobo e lobo, as it were?

When I first saw the film in 1994, my first assumption was that Stewart must have bitten or scratched Laura while he was tossing her around on the stable floor. While discussing it with my friends on the way home, we remembered the whole "passion of the wolf" thing, which made a lot more sense (because why would they have put that idea into the script if it wasn't going to play out in the story?). It's not that complicated a film, as much fun as it is, so the simplest explanation really is the best one.