The 'A-team' star, who is married to singer Justin Timberlake, said the unusual concept started as a kid when her parents let her decorate the home X-mas tree with the heads of her Barbie dolls, reported Femalefirst.
"My Barbie dolls didn't really stick around very long. I ended up mutilating them by pulling their heads off, cutting off all their hair, dyeing them with markers and sticking them on the Christmas tree lights. They'd light up like these demonic heads. My parents were very open.
"I still have the heads. They still go on every year at home," she said.
Scary decorations apart, Biel says she was a complete tomboy while growing up.
"I played any kind of sport - soccer, football. Whatever it was, I was playing with boys, hanging out," she said.