Bring up cloud formations at a party, and chances are you'll be left well alone for the rest of the evening.
But when it comes to "wave clouds" - as seen in Birmingham, Alabama recently - then you and your video-playing mobile phone may well be the centre of attention. For a couple of minutes, anyway.
The wave effect is called the "Kelvin–Helmholtz instability", and is caused by "a fast-moving layer of fluid sliding on top of a slower, thicker layer, dragging its surface", explains LiveScience.
In this instance it's simply a case of less-dense air (shearing winds) pulling on denser air, making for this astonishing sight.
The residents of Alabama - Alabamians, if you will - were so amazed by the phenomenon that a flurry of YouTube videos quickly hit the net, with kids no doubt trying to play the game of "What does that cloud look like?"
By us, it looks like a child's drawing of some waves or a piece of ornamental trimming on an ancient Greek urn - but whatever you think it looks like, one thing's for sure: it's pretty goshdarn amazing - and you can't say that about most clouds, now can you?