What defines creaminess, and why do people find it so appetizing? That's a mystery. But a group of scientists based in the Netherlands, using experimental vanilla custard, found that the dessert's creaminess depends on factors including its viscosity, homogeneity, and texture and surface appearance. One of the scientists, René de Wijk of Wageningen UR's Food & Biobased Research division, says test subjects were especially inclined toward custards that produce lower friction in the mouth. The same factors may apply to cheese, de Wijk says. Harold McGee, author of On Food and Cooking: The Science and Lore of the Kitchen, adds that the warmth of melted cheese provides its own source of pleasure.