Why didn't Clint Hill hear the first shot?

[Jarrett Smith]

I've been waiting to see if any of the LNs had a theory as to why Clint Hill specifically, but also other passengers in both limos, didn't seem to have either heard or recognized the first shot for what it was. I have speculated the roar of the accelerating motorcycles could have disguised the sound of that first shot but I wondered if others had different theories for that.

Clint Hill was drinking the night before and so were others.

https://www.newsweek.com/drunken-truth-about-jfk-assassination-391613

[John Corbett]

Hill heard the first shot.
He also heard the second shot.
He doesn't remember hearing the third shot as he had a lot on his plate at that moment, including stopping Jackie from jumping off the back of the limo.

By the time Jackie climbed out on the trunk, the shooting was over. That couldn't have been the reason Hill didn't hear one of the shots.