Why didn't David... [Spoiler]
So David is struggling with the knife with Sadie and the knife goes into her seemingly pregnant belly. David STOPS and apologizes!
Now, I get that he believed that she was pregnant and I get that under NORMAL circumstances that action would have been horrific. But in this case this psycho B**** had them all at gunpoint and was clearly trying to stab David. All bets are off then, it's survival time. I would regret the action but I'm not stopping until she is incapacitated.