Wine tears – the drops that form inside a glass after wine is swirled in a glass – are caused by the formation of an unstable shock wave
Source:
https://www.newscientist.com/article/2239298-we-now-know-what-causes-wine-legs-to-drip-down-inside-a-glass/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home