There’s a particular face people make when they swirl.

You know it.

The glass goes round. A film climbs the sides. Droplets begin their stately descent.

A small look of recognition appears.

Ah. Good legs.

And with it, occasionally, the suspicion that something rather profound has just been discovered.

It hasn’t.

Wine legs — or tears — are largely a demonstration of physics. Alcohol evaporates faster than water and has a lower surface tension. That difference creates movement in the thin film of wine coating the glass: the Marangoni effect.

Eventually gravity intervenes and the liquid runs back down.

Higher alcohol can make the effect more pronounced, although temperature, the glass and the wine’s composition can influence what you see too.

What legs do not reliably tell you is whether the wine is concentrated, expensive, well made or remotely interesting.

A modest 15% wine can produce magnificent legs.

A great Mosel Riesling may be considerably less theatrical.

The glass has no idea what you paid for the bottle.

So swirl away. It helps release aromas, and there are worse things to do with your wrist at dinner.

Just don’t read the droplets like tea leaves.

Observation is useful only when you know what you’re observing.