No, it's the Flehmen Response.
Have you ever wondered why your horse or your cat gives that "gurning" face after smelling something intensely? I did; I thought it was something in the smell that made my cat react that way, as if she didn't like it -- except she kept going back to it again. It seemed like she was a glutton for punishment.
Now I find it wasn't that at all: she was exhibiting the Flehmen Response, a way of smelling that does not involve the nose.
What it does involve is an organ inside the roof of the mouth called the vomeronasal organ, otherwise known as the Jacobson's organ. The "gurning" face (or, in the case of goats and horses, the weird lip-lifting) is actually a way of getting air to circulate inside the mouth so that the vomeronasal organ can pick up molecules of the scent in question. It helps the animal see what kind of scent it is, really, and gives them more information about the source of the scent.
Generally, the scents that cause this kind of interest are things that contain pheremones or other compounds that tell the animal about other animals, either of their own species or, in the case of cats, those of prey. Curiously, it is believed to be the basis of the Cheshire Cat from Alice in Wonderland.
"Flehming allows the animals to determine several factors, including the presence or absence of estrus, the physiological state of the animal, and how long ago the animal passed by. This particular response is recognizable, for example, in stallions when smelling the urine of a mare in heat." [wiki]
This is a small fact, something you can bring out in odd moments to impress your friends; but as an activity it rarely fails in comic charm. Here is a video of a pony with the Flehmen Response in action:
Lastly, I'm not certain the video below is a flehmen response (if so it's a very lively one), but it is pretty funny.
You can also type "Flehmen Response" into Google Images and see what you get: a veritable rogue's gallery of weird facial tics.