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: 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.
Why would the colony want Bill and Karen to join them?