One of the behaviors that is carried out quite often by lions, is known by the term Flehmen. The Flehmen response takes place when one lion, of either sex, sniffs and smells the urine of another. Chemicals and hormones contained in the urine elicit the Flehmen response. Usually, after smelling the urine patch on the ground or vegetation, the cat that is doing the smelling will lift his or her head, and hold their lips back in a strong grimace for a period of several seconds.
If you have never seen it happen before, it can appear to be a threat display, but in fact it has nothing to do with threat. Each cat has a vomeronasal organ (also sometimes called the organ of Jacobson) located above the palate. By sniffing deeply, and then pulling back their lips, they are in fact ‘testing’ the chemical content of the urine left behind by the earlier animal. Also, because lions are social for much of the time, it is easier to observe the Flehmen response taking place amongst members of the same pride. Although Flehmen is observed amongst males and females, it appears to be most important to males and it plays a part in allowing them to determine whether a female may be entering an oestrous cycle.