Even though he is not completely still, the sound of a thud combined with the sudden stillness is more than convincing enough to sell me the idea he is in fact grabbing something invisible and not just mere air
The sound mixing here is crazy good, but I gotta call out something most people missed: the camera's fixed focal plane on the 'air' takes this to the next level and really cements the realism.
I’ve seen a lot of people do the “invisible box” mime trick, but you’ve taken it to a whole new level with your sound design. It really does feel like you’re touching something. Very impressive.