When in the right mood, people are terrified by every curtain blown by the wind in an upstairs window, by what might be hidden by every approaching corner. The fear would be fueled by paranoia. I can't remember anybody since then who was as effective at exploiting unfounded or unrealized fear as Mr Serling, but this movie tries to recreate that sense of palpable tension that Serling loved. It starts in the normalcy of everyday irritations. People cut in front of other people in line, spill coffee on other people, carelessly bump into people, talk too loud in the theater.
People get irritated, they scare other people, or they are scared by other people.
The couple moves to different seats. We can tell that the black guys have forgotten the whole incident by the end of the movie, but Kyle is afraid to walk by them. Kyle walks to his car, and there is no reason for him to be afraid, but fear is in the air. The shadowy underground garage is filled with tension. The answer is nothing.