It's the below goof, read on:
"As the movie begins, the murder victim is heard to shout, and there is an instant cut to the murderers, who have just completed strangling the victim with the eponymous rope still around the victim's neck. If the victim was being strangled, he could not have shouted."
Well, this is not really a goof because as Rupert later explains towards the end of the movie, and he does give a detailed explanation on how he would go about murdering David, he explains that since the victim is pretty strong he would first hit his head very strongly with a heavy object, before finishing him off by strangulation. The head trauma is probably where David's scream comes from, which was probably not strong enough to kill him but he screams in pain.
Well, this is not really a goof because as Rupert later explains towards the end of the movie, and he does give a detailed explanation on how he would go about murdering David, he explains that since the victim is pretty strong he would first hit his head very strongly with a heavy object, before finishing him off by strangulation. The head trauma is probably where David's scream comes from, which was probably not strong enough to kill him but he screams in pain.