DPD motorcycle cop Jim Chaney was riding escort to the right side of the limo. He was the closest cop to JFK. Jim said that he thought the first shot was a motorcycle backfire. Jim Chaney said in a TV interview on 11/22/63 that he looked over at JFK right after he heard the shot and that JFK was looking towards his left shoulder. Here is a clip showing Chaney starting at Z136 through Z153. It appears to me that Chaney is turning his head to his left to look at JFK:

Unfortunately, I don't see Chaney's alleged head turn.
I see a headless motorcycle policeman riding his motorcycle, and I see Officer Chaney looking straight ahead after he emerges from behind a light pole.
EDIT ALERT FOR COMRADE STORING:
It is interesting, however, to see Secret Service Agent Glen Bennett in the rear seat of the follow-up car leaning far to his right to see if JFK is okay.