I always wondered about that morbid funny little face that my cats get when they sniff something sometimes, that little pause with their mouth slightly open...thanks to randomly opening a cat book to the right page while working at the library, now I know:
Flehman reaction: "The Jacobson's organ in the roof of a cat's mouth allows him to 'taste' smells. To use it, he opens his mouth a little--which looks as if he is grimacing--to draw air in for assessment. It is often used by tomcats to sense the reproductive status of females."
