Originally Posted by BevelDevil
I think I know what you're referring to, usually the down-the-line shot when she doesn't have much time to prepare. A lot of players do this, though I haven't really seen Federer do this.
I think it's a sign of arming the ball. It's definitely not her normal shot.
Federer uses a conventional Eastern. Henin used an Extreme Eastern, her knuckle rolled back by a half bevel.
Can't recall having seen Gasquet, Federer, Wawrinka, or Haas do it....and if they have, they certainly don't do it as often as Henin did it.