When Violet and Judy drive to the hospital in a panic, Violet parks her car at an angle taking up two spaces, but when she goes back to her car to put the corpse in the trunk, the car is parked perfectly straight within one space.
Just before the first time we see the garage door opener used on Mr. Hart (when Doralee is bringing his lunch in a green sweater), we see him walk into the bathroom looking for something - presumably a weapon. He is very clearly wearing pajama bottoms. When he walks out of the bathroom, he is very clearly wearing shorts (boxers?). He then breaks a leg off the TV tray, planning to hit Doralee with it. Much later in the movie, we see Hart walk into the bathroom - clearly wearing boxers/shorts - when he DOES find the nail file hidden in the drawer. Seems like there were two scenes shot, one in PJs and one in shorts, and they were incorrectly spliced together.
When Jane Fonda's ex-husband comes to the Harts back door at NIGHT and is let in they soon hear a noise upstairs. Mr.Hart has knocked over a lamp. When Jane goes to flip garage door mechanism and an ensuing tussle continues, the entire scene behind them is daylight. When she goes downstairs to let her ex out, it is once again night.
When Violet's car (with the three women in the front seat) wrecks into the Dumpster, none are wearing seat belts (we see them get into the car) yet none of them flies forward on impact, despite a high speed.