Final answer:
Mixing human hair with yak hair helps reduce the manufactured shine, giving a more natural appearance than when mixed with synthetic, sheep, or llama wool.
Step-by-step explanation:
Mixing human hair with yak hair helps remove the manufactured shine. Yak wool is a fiber obtained from shearing yaks, which, once processed into yarn, is known for its duller appearance compared to synthetic fibers. This characteristic makes it a suitable material to combine with human hair to achieve a more natural look. In contrast, synthetic fibers often have a noticeable shine that can give away their artificial nature, and wool from sheep or llamas also tends to have a more lustrous finish, which can contribute to the unwanted shine.