“The string is exceedingly interesting,” he remarked, holding it up to the light and sniffing it. “What do you make of this string Lestrade?”
“It has been tarred.”
“Precisely, it is a piece of tarred twine. You have also, no doubt, remarked that Miss Cushing has cut the cord with a scissors, as can be seen by the double fray on each side. This is of importance.”
“I cannot see the importance,” said Lestrade.
“The importance lies in the fact that the knot is left intact, and that this knot is of a peculiar character.”
“It is very neatly tied. I had already made a note to that effect,” said Lestrade complacently.

Arthur Conan Doyle (1892)