How could Hickey have not heard a nearby high-powered rifle shot at either "Z-124" or your beloved Z-148?
I've always heard, "Actions speak louder than words."
Regardless of the fact that he didn't remember doing it, why do you think Hickey started leaning over to look at the pavement in Z-146, even before your beloved jiggle-proved / misinterpreted-JBC-headturn-proved Z-148?
To answer your last question first, I have no idea what Hickey was doing because he never mentioned it in his report. He said he looked to his right rear upon hearing the first shot. I don't know how you tie that to his action of looking down to his left. That seems to be quite a stretch.
As for not hearing the first shot, or at least not recognizing it for what it was, that is not at all hard to understand when you take into account he was being straddled by four motorcycles, two to each side of him, and those motorcycles would be accelerating out of a 110 degree turn in order to keep pace with the limos. All four officers would have been on their throttles which would have created a very loud racket, maybe not enough to completely drown out the sound of the shot but certainly enough to muffle the noise to the point it wouldn't have sounded like a gun shot. If you have a better explanation for why Clint Hill and Jackie only remembered hearing two shots, I'd love to hear it.
Clint Hill's report also indicated the first shot he heard was the one that hit JFK in the back:
"The motorcade made a right hand turn onto Elm Street. I was on the forward portion of the left running board of the follow-up car. The motorcade made a left hand turn from Elm Street toward an underpass. We were traveling about 12 to 15 miles per hour. On the left hand side was a grass area with a few people scattered along it observing the motorcade passing, and I was visually scanning these people when I heard a noise similar to a firecracker. The sound came from my right rear and I immediately moved my head in that direction. In so doing, my eyes had to cross the Presidential automobile and I saw the President hunch forward and then slump to his left. I jumped from the Follow-up car and ran toward the Presidential automobile. I heard a second firecracker type noise but it had a different sound-- like the sound of shooting a revolver into something hard. I saw the President slump more toward his left."
Hill apparently conflated Elm St. with Houston St. in his report. Clint Hill's WC testimony tells much the same story if you want to read it:
https://www.jfk-assassination.net/russ/testimony/hill_c.htmIf Clint Hill didn't hear the first shot, why do you find it hard to believe Hickey didn't either.