Plot hole: Al comes home from work. He purposely doesn't look in the kitchen, so he can act like he's surprised it isn't Peg that brings him a beer. Steve talks and Al acts surprised that he's there. When you walk in the front door you automatically see the kitchen.
Plot hole: Al and Peg are upstairs with the killer. Both of them are screaming, but downstairs, you can't hear anything. Everyone is sitting around talking. It's not until Al and Peg scream again that everyone runs upstairs. And you can tell the screams were "on cue" also.