Revealing mistake: When Louis gives Gage the lethal injection, because the syringe is transparent you can actually see the prop needle retract in and out of the syringe as he supposedly injects Gage.
Revealing mistake: When Louis goes to give Gage the shot if you look closely you can see that the needle doesn't leave a puncture mark.
Revealing mistake: When Louis sets Gage's lifeless body on fire, it becomes apparent that it is a stunt dummy. The body resembles a small, pale mannequin with vague facial features and a wig.
Chosen answer: Church's behavior had changed after being buried. He was now violent (and working with Gage) and needed to be put down before killing anyone.
Bishop73