The beer was somewhat delayed. [Details of the research, including videos, see the website, from which the illustrations are taken, <a href="http://perso.ens-lyon.fr/nicolas.taberlet/washboard/,">http://perso.ens-lyon.fr/nicolas.taberlet/washboard/,</a> and the complete pdf at http://www.physics.utoronto.ca/~nonlin/preprints/TMM07.pdf.