Josh Hartnett at 2007 Film Independent's Spirit Awards - Arrivals, held at Santa Monica Pier, Santa Monica, California - 24.02.07

The Pearl Harbor star didn't have time to grow a proper beard for the horror drama, and spent weeks convinced his facial hair was all human.

He says, "They made the beard out of yak hair because it's curly, I guess... but they wouldn't tell me that. They told me it was made out of human hair, from some Eastern European prostitute's hair.

"It was the worst because... it would fall out and, if you were eating, you'd get little pieces of yak hair in your food.

"It's like yak DNA and no one tells you where the yak hair comes from on the yak."

Source: WENN