As the chocolate gets piped up through the system it experiences pressure-driven flow as its forced upwards against gravity. Then, as it flows over the domes, the chocolate thins, providing a good introduction to ideas like lubrication theory, a complex topic that tackles what happens as a liquid flows over a solid. But the most interesting concept is when the chocolate falls down from the dome in a curtain. Strangely, the chocolate pulls inwards, a phenomenon caused in part by the surface tension of the liquid pulling the chocolate sheet towards the interior of the fountain. While some aspects of the chocolate fountain are already easily explained, the authors note that "at a research level, the falling sheet leaves the greatest opportunity for further work."