Go to http://squarespace.com/stevemould to get 10% off your first purchase. I noticed that when I obstruct a laminar flow of water I get these ripples forming upstream like a standing wave. Here's my attempt to capture them on film and to explain them. It might have something to do with Rayleigh-Plateau instability. Twitter: http://twitter.com/moulds Instagram: https://www.instagram.com/stevemouldscience/ Facebook: https://www.facebook.com/stevemouldscience/ Buy nerdy maths things: http://mathsgear.co.uk/