How to give a fake slap? By Manon Murray.
INTRUCTIONS TO FAKE A SLAP (advice from Luc, Mirror Game actor)
1) Stand face to face, about a metre away from each another.
2) The slapper stretches and raises his arm like you're about to give a slap to someone who's taller than you.
3) The slapper pretends to give a slap to the other person. His hand comes very near to his face (it's a " / "movement).
4) A bit more difficult: the person who gets slapped has to be on perfect timing: he has to clap in his hands at the same time the slapper pretends to slap him.
5) At the same time, the other person turns his head like he just got slapped (eventually falls to the ground if it's a really big one).
Don't forget: the timing is extremely important, it won't look realistic if the person who gets slapped doesn't clap his hand at the same time he's supposed to get slapped.
UPCOMING: A video of Léa slapping Manon ("I've wanted to do this for six months!") Be patient.
Manon 
(Actually I can't put a video here, too bad...)