Forgive me for borrowing a couple of lines from an old Lynyrd Skynyrd song but that is what came to mind when I saw this. 😉
This Bighorn Sheep ram was clearly in the mood and was non-stop chasing a ewe around the canyon. She was not showing any interest and at one point stopped running to relieve herself. The ram got a good whiff of it and made this face.
This is in fact a behavior called the flehmen response. Many mammals will do this, curling their lips, raising their head and inhaling deeply allowing them to get a better sampling of a particular smell that interests them – kind of like a human taking a big whiff to smell something.