Dey wuz fishing and done lost duh bait.

If the dark/black/blue fibers were from John's Israeli wool shirt, there would be no doubt what those fibers were because wool is a natural protein fiber, easily differentiated from man-made fibers through microscopic examination and chemical analysis. The inner structure of wool fibers contain a core running the length of the round fiber and the outer layer is 'scaled.' Silk, on the other hand, is smooth and the fiber itself is triangular in shape with a solid core and the inner structure resembles a glass rod. Cotton fibers would have a rougher, hairier look than either of the other two fibers and man-made fibers are typically quite smooth. The proteins in wool contain carbon, hydrogen, oxygen, nitrogen, and sulfur that are combined into 19 amino acids linked together in ladder-like polypeptide chains.

Rainsong