The first player declares their initial letter, as if playing I Spy.
Then, they draw an initial subset* of a picture of what they had in mind.
The other players may call out at any time what they think the picture is going to be.
If one of the calls is correct, then the calling player
may finish the picture of that item (in as much detail as they like) before declaring their own initial letter and starting the next item.
However, if none of the calls is correct, then the first incorrect calling player must finish the picture, to represent the item called, not the item as imagined by the first player.
(I'm not sure who should start the next drawing in that case - possibly neither of them!)
*I haven't yet arrived at the best definition of this initial subset. The rules tested so far stipulated three strokes of the pencil, with the definition of one stroke being somewhat fluid at present.
The game is more interesting if, rather than starting a series of separate drawings on separate pieces of paper, the players try to integrate their items into a single picture, albeit a rather surreal one.
Under careful supervision, I believe this game may be a helpful mental exercise for somewhat nerdy children, in that it requires them not just to spot and extend a pattern (which comes easily to them), but also to keep re-defining that pattern in their own minds in response to the interventions of the other players (which does not come at all easily, but which is an important life skill).
Sadly, without careful supervision, those children are the first to burst into tears and/or violence in this game, for precisely that reason.