From 1964 through to 1988, one of the most iconic childrens’ programmes on British TV was Play School.

Hosted across its run by the likes of Brian Cant, Floella Benjamin, Derek Griffiths and Johnny Ball, the show consistently gave its viewers a mystery: which of the three windows would we be looking through this week? The choice was round, square or arched, and on the surface, it seemed to be a harmless, random guessing game.

Only it wasn’t. We’re indebted to Mark Kermode and Simon Mayo’s Film Review programme for this, as on last week’s episode of their show came the revelation that the choice of window wasn’t random at all. As a correspondent to the programme explained, the theme of the episode would determine just what shape window was chosen.

Thus, if the theme was something circular, such as wheels or balloons, then we went through the round window. Something like a window or a box, meanwhile, and it was the square window. The arched window barely appeared, meanwhile, and was consistently the wrong horse to back in this particularly guessing game. It took something like a fountain for the arched window to be chosen.

For those of us who used to sit diligently and guess, this will, no doubt, be a painful revelation…

This is all backed up by the BBC’s own trivia page for the show, that you can find right here: BBC