One reason that it is funny is that it plays against that.

We the audience maybe forget for a moment that we are not watching real life. We are watching a drama or entertainment. So we expect something relevant to happen. That’s the convention.

The exchange plays with that expectation. It deliberately forces us out of our pleasant illusion and makes think us about our real experience - we are sitting in a seat and watching a performance, which is happening at that moment.

And nothing happens, just the same as real life

(ROS and GUIL ponder. Each reluctant to speak first.)

if the dialogue should be clearly about who speaks first, wouldn-t the stage direction have been something like:

(ROS and GUIL ponder. Each reluctant to speak first. ROS tries to say something but does not) ?

i mean - you could play it like that. But then to me some of the beauty of that dialogue is lost, that comes from the fact that for the spectator it-s not clear what is the subject of it.

It's the antithesis of Chekhov's Gun.

It starts off with G thinking R has said something, but G is wrong - R didn't say anything. It ends up with G telling R he hadn't said anything, but again G is wrong, G started the whole thing off when he says Hm?

This is funny because R ends up thinking he'd imagined G saying something when infact the opposite happened.

It fits the characters well with G frequently being clever with no common sense and R having common sense but not being terribly smart.