Pattern formation in hot chocolate

Found these patterns in my mug whilst working late one night :). Hope to model the pattern formation with fluid dynamics at some point.

Useful papers:

• Nonlinear dynamic and pattern bifurcations in a model for spatial patterns in young mussel beds - Rong-Hua, Quan-Xing, Gui-Quan, Zhen Jin and van de Koppel  
   http://rsif.royalsocietypublishing.org/content/early/2009/02/09/rsif.2008.0439.full.html#
  
  
• Pattern Formation in Draining Thin Film Suspensions - Buchanan, Molenaar, de Villiers and Evans
  http://pubs.acs.org/doi/abs/10.1021/la063282a