Ugh...unfortunately this just connected some dots for me. I have been contemplating that JRH was actually intending to drive all the way to the movie theater and either "discover" Cooper when parking or actually go in to the movie and do a big dramatic exit when LH called from the daycare. But I couldn't figure out why he stopped at the shopping center if this was the case. I thought maybe the smell had gotten too strong. But now I can picture it: he's driving, knows Cooper is in the back seat presumably deceased. Suddenly he hears a sound. His heart stops for a second and adrenaline rushes in. He thinks Cooper is still alive somehow and choking on something, so in his fear he actually has a normal response which is to seek help immediately, so he pulls in to the shopping center, jumping out yelling for help because his son is choking, pulls him out of the seat and realizes C is definitely deceased. Panics again because the scenario he planned has changed. Tries to reach LH on her cell and then by calling the daycare center. Gets mad because this isn't what he had planned and mad because that sound scared him so bad.
Explains some of the anger behaviors at the scene. It's so upsetting to picture this. Poor Cooper.
Actually, you SEE a person choking, you do not hear them. A person choking doesn't make much of any sound because their airway is blocked. One of the first things you are taught in learning the Heimlich is to ask the person in distress if they can speak.
I think Harris used the choking excuse to explain why he stopped and got help. I think it was Harris' own gag reflex and choking reaction to the horrific smell that made him stop. Cooper was in that enclosed, hot car right after eating and he may have vomited.
How to perform the Heimlich maneuver:
First ask, "Are you choking? Can you speak?" DO NOT perform first aid if the person is coughing forcefully and able to speak -- a strong cough can dislodge the object.
http://www.nlm.nih.gov/medlineplus/ency/article/000049.htm