Last week, Neil LaBute's The Shape of Things at the Almeida didn't have a curtain call, which made this premiere the most oddly shaped show in the country, if also one of its hottest tickets. How brave, you may think, if difficult on the actors, who are deprived of those final bows that act as a traditional salve to the thespian ego (although one of the cast, Frederick Weller, who does not appear in the final scene, says he loves the chance to grab the best seat in the bar).

Since then, things have changed. As of last Wednesday, and at writer/director LaBute's behest, the nightly bows are being left to chance; during each performance, the deputy stage manager picks a 'yes' or 'no' out of a hat. 'Yes', and the actors bow; 'no', and they don't.

In retrospect, perhaps LaBute recognised his initial decision to dispense with convention as self-aggrandising and self-important: we're so searing, the gesture appears to say, that we don't need anything as trivial and bourgeois as a curtain call, though, in my experience, actors' bows have never previously diluted the impact of King Lear or Medea.

'I think Neil likes to do things simply because they amuse him,' Paul Rudd, one of the actors, told me. 'The play ends on something of an abrupt, uncomfortable note,' he adds, 'and then the actors don't come out, and that resonance stays with you.'

Bows, however, needn't simply boost an actor's self-esteem. The curtain-call is part of the unspoken contract between spectator and event, signalling closure. But one can seal an evening, as it were, with applause without in any way vitiating the impact of what has gone before, which is why LaBute's decision suggests that he may not fully trust his script. Or maybe because he also directs films, his head is still at the movies, where audiences that do clap always look slightly foolish.

In my years of theatregoing on both sides of the Atlantic, I've only once before encountered an absence of a curtain-call, and that was at a 1976 Lincoln Center production of The Threepenny Opera, directed by Richard Foreman, a doyen of the American avant-garde. On that occasion, Raul Julia and his colleagues slunk offstage following a final reprise of 'The Ballad of Mack the Knife', only to have the house lights immediately go up, leaving the audience no choice but also to slink out.

Other productions before my time have made this same brutal choice. Peter Brook ended his anti-Vietnam piece, US, in 1966 with the cast simply staring down the audience, neither bowing nor making any move whatsoever.

Two years later, Brook's National Theatre Oedipus, with John Gielgud in the title role, ended not with a company bow but with the emergence on stage of a six-foot golden phallus. 'No one we know, is it, dear?' the actress Coral Browne reportedly asked on opening night.

LaBute's landscape is too grim for such cheekiness, even if his play does have its own phallocentrism, with the music of the Smashing Pumpkins making its own aggressive statement from the start (and sending the Pinters fleeing from the auditorium before the show began).

As a result, its exemplary cast has had to suffer the audience's distaste (in Rachel Weisz's case) or pity (in Rudd's) without the communal release of a bow. So if you do glimpse the company by the bar, and the National Lottery that night has come up 'no', why not give them - or even buy them - a round?

LaBute may render them pawns in some larger statement, but the fact is they're bloody good.

Matt Wolf is London theatre critic for Variety