Sir, I was fascinated to read the recent letters in the BDJ regarding 'oil pulling' - the process of using cooking oil as a mouthwash, its efficacy apparently proved by the way the oil takes on a milky colour after a few minutes of vigorous swishing. However, it has occurred to me that we are already familiar with a similar process used for many years albeit on an industrial scale rather than intra-orally. We substitute the oil with milk, the process is called churning, and the net result is butter. Just to clarify (pun intended), according to Wikipedia the change of colour is due to the transforming of a fat-in-water emulsion (milk) to a water-in-fat emulsion (butter) rather than any magical healing properties. As regards the research that was reported in one of the letters, the oil was only compared with water, so it could well be that other viscous liquids may give a similar improvement - may I suggest jelly and ice cream as a possibility for further research? (sugar free of course).