After Slaughter runs Hoffo's car off the road, Hoffo's face is covered with blood. When Slaughter shoots the gas tank, and the car is surrounded by fire, Hoffo's face can be seen to have only a little bit of blood on it.
Rip Torn not holds the Luger with which he shoots Don Falice incorrectly, he actually blinks both times he fires it indicating that he had no experience =, nor training, in the use of firearms. Considering that he's supposed to be a prolific killer, this makes no sense.
A character uses a revolver with a suppressor attached. Revolvers cannot be suppressed (other than a specially manufactured Russian model) because most of their noise comes from the cylinder gap before the barrel which is behind the suppressor.
At the very beginning of the film, Slaughter's father is seen sitting in his car, turns the key, and it explodes. The entire car is engulfed in flames, which shoot 20 feet into the air; the camera lingers on the inferno. The very next scene, we see Slaughter sitting in the ER. The doctor comes out of surgery and tells him that his father didn't make it. I'll say...the man was cremated.