What’s the deal with wine “legs”?

Hello there! I'm Dr. Vinifera, but you can call me Vinny. Ask me your toughest wine questions, from the fine points of etiquette to the science of winemaking. And don't worry, I'm no wine snob—you can also ask me those "dumb questions" you're too embarrased to ask your wine geek friends! I hope you find my answers educational, empowering and even amusing. And don't forget to check out my most asked questions and my full archives for all my Q&A classics.
Dear Dr. Vinny,
What’s the deal with wine “legs”?
—Stephanie, Lake Sherwood, Calif.
Dear Stephanie,
If you swirl a wineglass and stare at it afterward, as the wine settles, you might notice translucent streaks of wine clinging to the bowl of the glass. Those are “legs,” sometimes also referred to as “tears.”
Legs happen in part because of what’s known as the Marangoni effect: The swirling causes some of the alcohol to evaporate, pushing the surface of the rest of the liquid up the sides of the wineglass. Contributing to the effect are shock waves passing through the liquid because of math.
While it might be observant of a wine connoisseur to notice these legs, they don’t offer any indication of quality. Folks once thought that wines higher in alcohol or sugar might have more prominent legs, but the shape, speed and volume of the legs are influenced by many factors, including sugar and alcohol but also temperature, (of both the wine and the air), humidity, glass shape and more. All wine has alcohol, so all wines have varying degrees of legs.
—Dr. Vinny