Earlier today I present you the following counter-intuitive puzzle, about a curious object that fits through a small hole but not through a large one. Here it is again with solutions.

## Less is more

Design an object that cannot go through an open window, but through one that is almost half closed.

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

**Solution**

Here are three objects that fit the bill. They all go through turning the closed (or nearly closed) frame. The simplest shape has a cross section of three sides of a square:

(If anyone is looking for homework, could someone calculate the exact dimensions of the form, in relation to the width of the window, the thickness of the frames and the angle of the partially closed frame, and post them below?)

The V shape also works:

The C shape is possibly the most elegant. Here are two videos showing how it can’t get through the open window, but can when one of the windows is flush with the wall.

Thanks QuanticA Russian math magazine for school children, for today’s puzzle.

One last thing: my new book is out on Thursday. *Think twice* is a compilation of counterintuitive puzzles along with explanations of why they trip us up. If you enjoyed today’s challenge, I’m sure you will!

*Think Twice: Solve the Simple Riddles (Almost) Everyone Gets Wrong (Square Peg, ££12.99). To support the Guardian and Observer, order your copy from guardianbookshop.com. Delivery charges may apply.*

*I’ve been doing a puzzle here on alternate Mondays since 2015. I’m always on the lookout for great puzzles. If you want to suggest one, email me.*