I was up on the Skeena earlier this summer, and the preferred sockeye “fly” used for flossing was a red Gammy about a size 4 -6, with a thin piece of orange egg yarn tied above the eye and knot.
The guys would take the red Gammy, and tie it on to their leader. They’d then cut about a 2 inch piece of egg yarn, take a strand of that 2 inch piece that was about a quarter of the original diameter, then wet it with their mouth, roll it until it was quite thin, and then tie it just above the knot with an overhand knot, trim it to about the length of the shank and start casting.
The theory was that the yarn would get stuck in the sockeye’s teeth, to help hook up, but I met a guy using bare hooks that was just as successful. I did see quite a few fish hooked in the mouth, but there were also quite a few that were foul hooked
Not to pass judgment, on those who do it, but I never felt comfortable with the process, and decided to target other salmon instead.