Revealing mistake: When the two station reporters are investigating Eddie's room, as the female bends down to the table, she is scared by a dog. In one shot you can see a black wire on the dog. (00:14:55)
Revealing mistake: The final shot of the sex-scene between Bill and Marsha is very obviously a piece of (rather cheap-looking) 2D cell animation. The actors look like cartoons, the fire is simply the same few frames repeated over and over and the background looks obviously painted.
Answer: Whether it be dog or wolf, the primal instincts take over. Every creature, in nature, has an urge to seek out their own kind. When the husbands were bitten, they are consumed with the desire to hunt, kill and mate.