If you use bricks as dominoes: you get a second wave going in the opposite direction. Watch the original brick domino video here: https://www.youtube.com/watch?v=-BTWiZ7CYoI I think that is the original upload. If anyone finds a better one, please do let me know. Support me on Patreon and help me make more videos like this. https://www.patreon.com/standupmaths CORRECTIONS - The overlap length should be 21 - √(21² - 6²) = 0.875 cm not the incorrect √(21² + 6²) - 21 = 0.84 cm I show on-screen. First spotted by Daryl Adriano. - A correction to my masonry terminology! What I called the width is actually the height of a brick (which makes sense given the orientation bricks are normally laid). The width is the third dimension: how far into the wall they reach. Thanks to Doodle Vids. - Let me know if you spot anything else! Music by Howard Carter Design by Simon Wright MATT PARKER: Stand-up Mathematician Website: http://standupmaths.com/ Maths book: http://makeanddo4D.com/ Nerdy maths toys: http://mathsgear.co.uk/