But if you utter this our business, then we shall be guiltless of your oath which you have made us to swear.
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.