In an article Phys. Rev. Lett. 100, 024501 (2008) Nicolas Bremond, Abdou Thiam, and Jerome Bibette are studying coalescence of the emulsion droplets (sizes on the order of tens of microns) in microfluidic channels. What they find is that coalescence of the droplets happens when the dropets begin to separate, and proceeds in a cascading “chain reaction” of sort, with an entire train of particles coalescing together, once the first pair of particles start merging.