Hair was one of the really hard problems, in computer graphics. They tried to "cheat", at first, but it looked super weird, so they had to simulate individual hairs... became possible with enough computing power. "Little Red", the 3 min animation Pixar presented at Siggraph 1987, had taken 1 year to produce. To calculate 140'000 individual hairs would have taken a million years 😅 https://www.youtube.com/shorts/izV2ppX-kw8