Continuity mistake: When werewolf Eddie takes the file from Terry's hand, while she's on the phone, the phone drops from her ear, to the floor, twice between shots. (01:00:45)
Continuity mistake: When werewolf Eddie takes the file out of Terry's hand, he holds it at the top. In the next shot he is holding it at the side. (01:00:50)
Continuity mistake: When the werewolf attacks Terry, it pushes things at her; note the pedestal which flies into her - the white sheet falls off of it. In the very next shot the sheet is back on the pedestal again. (01:01:00)
Continuity mistake: When Karen enters Dr. Waggners office, the phone on the desk is right by the edge, closer to the door. After Karen finda Terry's corpse, the phone is now on the other edge of the desk. (01:03:00)
Continuity mistake: When Karen enters Dr. Waggner's office, she leaves the door halfway open. After finding Terry's corpse, the door is now almost shut. (01:03:00)
Continuity mistake: When Karen finds Terry's corpse, there is nothing visible on her, and half her body is shown. In the next shot a white blanket is suddenly on her body, all the way up to her neck. (01:03:15)
Continuity mistake: When Eddie is transforming into a wolf in front of Karen his left hand turns grey and grows hair down to the knuckles. Then in the shot of his arm muscles expanding, his left hand has a normal skin color and hair only down to his wrist. Apparently, while editing no one checked to see how his hand was already established. (02:09:55)
Other mistake: At the end after the barn fire, Marcia is at a tavern, ordering a rare steak. While it is believable that she escaped the barn fire, it is unbelievable that she is in the tavern wearing the same dress and necklace she wore prior to her transformation in the barn. All of her attire would have been rended in the transformation and lost in the fire. Unless her wardrobe consists of duplicates of the same clothing.
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.
Factual error: The rifle which Dennis Dugan's character is using has to be reloaded before every shot. Still, when he shoots Slim Pickens, he somehow manages to hit him with two bullets within a second.
Answer: I think they were purposely brought there to both join the colony. Marsha, who desired Bill, was impatient and bit him. As for not being mad at her, the Colony was slowly turning to her leadership, instead of the Doctor's compassion treatment.