Actress MICHELLE WILLIAMS sprained her ankle on the third day of shooting Brokeback Mountain when a sledding scene turned disastrous.

Williams and real-life boyfriend Heath Ledger had to sled down a hill when they were thrown from the toboggan - and the actress had to be taken to hospital.

Cinematographer RODRIGO PRIETO recalls, "On take two, the sled flipped, and Michelle really sprained her ankle and had to go to the hospital.

"We were only on our third day (of shooting) and we temporarily lost our main actress."