What are the drips of bourbon that run down the side of the glass called?

The drips of bourbon that run down the side of the glass are referred to as "legs." This term describes the way the bourbon interacts with the surface of the glass after it has been swirled. When the liquid is swirled, it coats the glass and forms droplets that slide down; these are the legs. The formation of legs can be influenced by the viscosity and alcohol content of the bourbon, and the presence of other compounds that can create a film on the glass.

Understanding the visual aspects of bourbon, such as the legs, helps bourbon stewards assess the quality and characteristics of the spirit. Observing the legs can provide insights into the bourbon's mouthfeel, richness, and body, as thicker legs may indicate a higher alcohol content or more oils present from the distillation and maturation process.

Other terms provided in the choices, such as fingers, traces, and rivulets, do not accurately capture this specific phenomenon as they are not commonly used in the context of bourbon tasting. Thus, "legs" is the correct and widely accepted term for this observation in the bourbon tasting experience.