The Laughing Man

Somewhere on the web is an interview with Robert Culp about the making of the movie. He explains that a lot of the location shots were done with out permits etc, and that the laughing garbage men, I think he calls them, were not planned, but got picked up on the sound track. Not sure why they didn't overdub, but it sounds like a "mistake". But it's still fair game for interpretation, sorta like the big guns that don't shoot straight or the angry father figure of a police Lieutenant? Were they really just hoping for Dad's approval? Is that "what it's about"?
Culp was too particular of a writer/director for anything to be a mistake. Best scene in the movie is Boggs buying another T-bird. Does it run? I'll take it! He doesn't even kick the tires. Perhaps a commentary on Boggs' basic sunny optimism and trusting nature? I mean, who would expect an honest answer from a used car salesman? Obviously a hard boiled,cynical private detective!