Deliberate mistake: Beth shoots Bryce three times in the chest, and he falls face down on the floor. She then drags his body across the floor, also face down, to in front of the sliding door, but there is no sign of blood anywhere.
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Suggested correction: In the early Seventies, no television show used blood effects. They were too expensive and would severely restrict potential audiences as television channels were notoriously conservative in those days. This is a creative and technical decision, not a mistake.