Today’s puzzle is about defenestration. Now there’s a word I’ve never used in this column before.

Less is more

Design an object that cannot pass through an open window, but can pass through one that is almost half shut.

Here are illustrations of a cross-section of the window that make it clear what is required. The wall is blue, and the two sashes are orange.

The problem looks ridiculous – how can something fit through the smaller hole, but not the bigger one? It seems to defy common sense!

Yet there is an object – or possibly several – that fit the bill. Can you think of what it might look like?

And what about if the left sash was completely closed, making it flush with the wall – can any objects that cannot pass through the opened window now pass through?

I’ll be back at 5pm UK with the solution. Meanwhile NO SPOILERS. Instead discuss your favourite windows.

Source: Kvantik, a Russian maths magazine for schoolchildren.