"Look of terror" downgraded to "pained or startled look".
The descriptors "terror" or "pained" or "startled" are different ways of describing JFK's look in z225. The look is consistent with something unexpected and unpleasant happening to him and inconsistent with him just deciding to stop smiling and waving. The timing also tells you that because the chance of him reacting to something sudden and unpleasant 55 ms. before, but unrelated to, his reaction to being shot seems rather unlikely.
Connally says that in the same breath he's talking about his viewing of the Zapruder frames.
I was just pointing out that he may not have realized that there was a significant difference between appearing from behind the sign in the zfilm and actually passing the sign. No one bothered to ask him. This was one of the problems with the WC: there was no counsel taking an opposing position and asking probing questions, such as I have suggested could have been asked.
I think Greer's two turns between Z280 and Z271 are really one.
??271?. Did you mean z291? If so, I agree. He remains turned from z280 to z291 because we can see the top of his head remaining in the same position. It is not in that position in z279 and before that we cannot see Greer's head as it is blocked by the windshield frame/sun visor. There is no other turn until z301-303 which lasts to about z317. So the turn at z280-291, which is when JBC falls back onto his wife, is definitely the one before the third shot and the one he described as having been made immediately after the second shot.
Greer just momentarily looks ahead to check his steering. Greer simply didn't remember the brief turn forward, or thought it unimportant. His head is largely hidden by the windshield and rear-view mirror in many of the frames between the Stemmons sign and the Z270s, so he could have looked back earlier than Z280.
Yes, he could have looked back earlier but he would not have seen JBC falling back onto his wife then. He described his last two turns in relation to the shots he heard. On the first of those last two turns, he saw JBC falling. That has to be the turn from z280-291. He turned forward beginning about z291 and turned back again from z301-303, less than a second later which is when the third shot occurred.
Kellerman said he turned around to see the President with his hands at his throat. He does a sharp leftward head-turn about Z252-Z290.
Mr. SPECTER. You just indicated that you had turned to the left.
Had you turned to the left after hearing his voice?
Mr. KELLERMAN. Yes; certainly.
Mr. SPECTER. And what did you see? You have described what
you saw in terms of position of his hands.
Mr. KELLERMAN. That was it.
Kellerman did not indicate there was a shot fired while he was looking backwards.
Kellerman is looking back while JBC is falling back onto his wife. He didn't comment on seeing that either.
"Computer says: No."
You did a 3D model to prove this? My computer says your computer hasn't done its homework. Anyone looking at your supposed 3D view will see that the trajectory through JFK is left to right, not right to left:

A left-to-right shot could not have come from the TSBD.
I think Hickey is probably talking about the headshot ("hair flew forward"). Could have heard the impact on the head and the sound of the rifle report a split-second later as two shots ("there seemed to be practically no time element between them"). Kennedy's head went backwards and to the left, sort of in the direction of Hickey, so he would have perceived less of the head snap and more of the hair (scalp) flying away. Hearing the rifle report, he then sees the President's much-larger overall movements and thinks it's a reaction to a bullet strike.
Hickey couldn't see the little hair flutter in the Z270s
Hickey would have disagreed with you. He said he saw it and he was not looking forward until after z256.