Why does Gael Monfils always open his hands every time he serves?

Why does Gael Monfils always “Open his hand and twirls and bends his fingers backwards” whenever he serves a Tennis ball?

Verulam 12019-08-18T08:18:53Z

I've never noticed this but you might as well ask why does Nadal have to go through his 'routine' every time he serves, or Djokovic bounce the ball SO MANY time before he serves?? It's what players feel most comfortable with.