On Saturday, I went to another performance of the Chekhov play that I discussed a couple of days ago. And this time, I was struck by something that was neither in the play's text nor in the performers' interpretation, but rather in the audience's reaction.
There was someone in the back of the theater with a loud and infectious laugh, who didn't laugh at any of the obviously funny lines, but instead laughed — maybe a hundred times — at a selection of lines that is not easy to characterize. And laughter being the sort of thing it is, a few other audience members would erratically join in, few enough that the individual characteristics of their laughs soon became familiar.
The laugher's interventions mostly seemed to me to be points where a character changed the subject, or said something that was unexpected in the context of the previous discourse, or said or did something awkward or socially uneasy. These are traditional occasions for nervous laughter, though usually not so regular or so loud in a public setting.
But there were other theories. One person thought that the laugher might have been a friend of a couple of the actors, who reacted whenever one of them entered the on-stage conversation. Another theory was that the laugher was reacting when the actors made certain expressive faces. These are obviously overlapping theories, and many others might be devised as well.
The actors reacted in different ways, which reflected their characters' characters, and (IMO) helped save the performance. Natasha glared in the laugher's general direction, as if he'd left a dirty fork on her parlor table; Irina slumped dejectedly, as if this were one more evidence of the stupidity of her provincial surroundings; Masha seemed to be on the verge of cracking up, and (perhaps because of her attempts to suppress a fit of giggles) developed a brittle, sardonic smirk that suggested how close her character was to cracking in a different sense of the word.
Normal laughter is actually rather weird and hard to explain, but because it's familiar, we don't generally recognize how odd it is. It takes an abnormal laugher, like the one I encountered Saturday night, to bring this point out.
As an empirical sort of person, I wish that I had a recording of that performance to analyze, to see how well my memory accords with the facts. And in fact, a corpus of audience reactions to performances in smallish theaters (this one was an audience of 80-100) might shed some interesting light on the individual and social psychology of laughter.