Weird dumbbell exercise - What are they doing?

Coquette6

I've seen multiple guys at the gym doing this and my curiousity has just gotten the better of me, so I have to post here to see what it is and why they're doing it. They're standing up and have a dumbell in each hand. The upper arm and elbows stay still and close to the body, with the elbows bent. Then they flap. Or clap. Or something like that, I don't know how else to describe it. They bring the dumbbells together like they're clapping, then bring them out in line with their body again. And repeat. What are they doing??