Crosswords exercise our little grey cells, of course; and they test our vocabularies and general knowledge. But the urge to solve a crossword is about more than mental gymnastics. Humans are, by nature, problem-solvers. The impulse that led us to the wheel, also brought us the crossword. And we love the crossword because, unlike so many things in our complicated lives, the puzzle is solvable and finite: there is a right answer. The crossword allows us to bring order to chaos. It challenges, absorbs, comforts and distracts us. As Martha Petheridge, the first female editor of the crossword puzzle, said at the height of the Great Depression, “Who can worry about the rent when you are trying to solve 25 down?”.