 This is a mathematical snack from the Association of Teachers of Mathematics. I have some tiles, and I want to use those tiles to tile a rectangular floor. The tiles are made up of two squares, like a domino, and I want to make my rectangle so that it has no fault lines. Look, there's a picture here. There's one tile, another, another, another, another, another. But I've got a fault line running all the way through. It's a crack, which runs from one side to the other. Now I'm going to see if I can make a rectangle with no fault lines. I could draw them on paper like this, and I've done that. I've made a rectangle, but look, it's got a fault line running all the way through it. Can you see that fault line? I'm going to choose to do this using dominoes. You can either use paper to draw on, you can use dominoes. Here are my dominoes, and that was the one I just did. Look, can you see? It's not quite the same, but it's got a fault line in it. I'm going to keep building. I'm going to put one across there and one across here and one across here. I've now made a rectangle. But look, it's got a fault line going all the way through there. What's the smallest rectangle you can build with no fault line? What's the smallest square you can build with no fault line? And I wonder if I could cover a chess board eight by eight squares with no fault lines. There's the challenge.