To be fair, Rohmer did not invent this pattern, just modified an existing one by changing the material. The mohair/angora goat leech is a very old pattern. It can be tied with any long fiber dubbing, whether natural or synthetic, or with mohair, which is angora goat yarn. I personally prefer STS Trilobal for these because it is not as flashy as Semi-Seal, but have some of those as well, for murkier conditions.