Pitch Black (2000) ending / spoiler
The group don't understand why the aliens can keep track of them, that is when Riddick explains them that Jack is a girl not a guy and that she has her period and the aliens are smelling HER. The fight and run for survival ends with only three survivors Riddick, Jack and the Islamic Cleric when the manage to get off the planet in the skiff. Then they decide to tell whoever they meet that Riddick died on the planet to give him some freedom.
Submitted by Jack