It sounds like a party trick: Add water to the clear, licorice-flavored ouzo liquor, and watch it turn cloudy. This ‘ouzo effect’ is an example of an easy way to make highly stable emulsions — or mixtures of liquids that don’t like being together, like vinaigrettes — but nobody has yet fully understood how it works. Now, researchers report that the secret may lie in the unique structure of the emulsion’s droplets.