Apple Watch Face Showing ‘Kissing’ Watch Faces

I have a Series 9 Apple Watch. Tonight, for no apparent reason, it vibrated and, when I looked at it there was a grey on black animation that looked like two watch faces moving from nearly horizontal to vertical and back. Each time it looked like the watch faces were touching (kissing). They did this for three, no more than five times before returning to the normal watch face.

I wondered if there was anyone else who’d seen this and if they know what it means? Or maybe I’m just having hallucinations?

Thanks, in advance for any information anyone has.