They are acting, of course.Jace-BeOS wrote: The body language of both people being knocked over is too funny for me to be willing to accept it as real
IMO this was a planned gag, i.e. they filmed the scene without really throwing anything (except themselves on the ground) and then editing the rest in later on to make it look like something thats bouncing back from the window knocks them both out.
Of course i could be wrong, but that would be my guess.