I had seen people complain that if Harlan had listened to Martha, he would still be alive; but I think people are forgetting the information he had at hand.
Martha didn't know about the change of the will, but Harlan did. He knew if the ambulance said he was dead by the time they arrived, and the will showed she got the money, she would for sure be accused of purposely killing him rather than negligence. She would go to jail for an accident, even if he clearly didn't mind dying then or for said accident.
So he said fucked, I am not letting anything happen to you or your family.
As calm as he was seeing, he probably thought he only had a few minutes before the symptoms would kick in, and that Martha would not do anything to save herself from this; so he needed to act and act fast. He took into consideration what he knew, and ran with it before anything could go awry.
I can't stop thinking of how he didn't doubt to slit his throat, just so it would look like suicide (Which technically it was) because he would rather slit his own throat than let Martha pay for this.





