When David Vanowen (Ford Austin) returned the money to the box in his backyard, he had placed it in a black garbage bag., and then nailed the box shut. When he opened the grave again, the money was not in the bag, but stacked loosely in the box. But then, the next day, the money in the grave is back in the garbage bag.
When David Vanowen (Ford Austin) disposes his clothes in a dumpster after he was fired, he's shown wearing a clean white t-shirt. But when he gets back in his car to drive away, the shirt is blood soaked at his right shoulder.
When David is talking about installing his own septic, this is very illegal. Soil tests must be made, the water table height must be determined and several permits are needed for installation of a septic system.