"I'm going to kill you........................" click.
Just a creepy scene. Billy is babbling incoherently over the phone and Barb is having none of that and is giving it all back to him. Then, out of nowhere, he says in a normal but serious voice "I'm going to kill you" and then hangs up. For a second you can see Barb is a little nervous about it. It made her uneasy. It just goes from one side to the other. Imagine getting that obscene phone call and then out of the blue the person on the other end is talking normal and utters those words. That would make anyone a little uneasy.
I find that is something missing from today's movies. That is such a simple line and it just sets the tone for the whole movie.