When I first saw this I wasn't quite sure what was going on, but, after some research, I determined that the bison in the above photo performed what is known as a
flehmen response.
While at first this rather grotesque posture may in some ways resemble the famous photos of Hugh Jackman running on a beach, I assure you humans do not exhibit flehmening.
A flehmen response a form of olfaction (i.e. smelling something) using sensory organs other than the ones more frequently employed in normal olfaction. As shown in the photograph below, when a bison uses its main olfactory system, it raises its nose and sniffs the air.
However, when a bison uses flehmening it will extend its face forward and raise its upper lip. According to wikipedia, this response is often used to detect phermones.
