There is nothing anomalous in pointing out human (physically limited) abilities. One way to prove/disprove this is by reproducing the action and comparing it to the extant films using the allotted time given. So, how does Jackie in Nix(elbow lowers onto trunk lid in last frame) slide back into her seat as we see in Z (z411-z417) in 6 zframes = 1/3rd of a second? Remember, as she turns towards the back seat, she has to contend with JFK’s dead body weight, which is already crowding