It shall be, that whoever shall go out of the doors of your house into the street, his blood shall be on his head, and we shall be guiltless: and whoever shall be with you in the house, his blood shall be on our head, if any hand be on him.
That "scarlet thread" so prominent in this narrative was surely a very strong and efficient rope, capable of carrying the weight of a man.  A red rope is certainly unusual, and we cannot entirely overlook the connotation throughout history of the color red, often associated with brothels.  "The red light district" is an expression still known in many places.