I made a giff of 37 Nixian frames. It appears that Ready & Landis do indeed simply fall/lean forward due to Queen Mary braking. McIntyre also leans a little.
The "dark shoes" seen under Queen Mary are probably due to Ready's & Landis' own shadows on the tarmac.
Plus there are some shapes or something that are probly simply due to reflexions from the shiny running board on the near side.
Ready can be seen steadying himself by placing his right hand on the bonnet.
Near the end Ready has mostly stood back up again.
Thanx to Jerry Organ for pointing out my error.