Referring to this portion of Phil Willis's testimony: "when the first shot was fired, she turned to the right toward him and he more or less slumped forward" ....
that would therefore be the shot at Z224.
I think seeing the Z226-228 slump would be considered witnessing a "hit" (or the reaction to a bullet strike).
Mr. LIEBELER. Did you think that the President had been hit by the first shot?
Mr. WILLIS. I didn't really know, sir.
Mr. LIEBELER. You couldn't tell whether he was hit by the first shot? You couldn't tell whether he had been hit by the first shot or the second shot or the third shot, or by how many shots he had been hit?
Mr. WILLIS. No, sir.
From the Clay Shaw Trial:
Q: Mr. Willis, did you have occasion to see any affect
that any shot may have had on any occupants in the
Presidential limousine?
A: Honestly, no, sir, because I was trying to use the view
finder for the camera and I was more interested in getting
the whole car than focusing on an individual. I did not.
I'm pretty sure his view to the President would be blocked by the Z220s. I think more of the Secret Service limousine would be between Willis and Kennedy by then.
So if Willis in his testimony is describing that he witnessed a non-hit "slump" prior to taking his Z202 slide, it could be this.
Willis would have seen this small forward slump from behind, and so would not know the President was smiling and not distressed. The animation is slowed.