male and female may be evicted. Lions of both sexes may be involved in group homosexual and courtship activities. Males will also head-rub and roll around with each other before simulating sex together. Health and mortality Although adult lions have no natural predators, evidence suggests most die violently from attacks by humans or other lions. Lions often inflict serious injuries on members of other prides they encounter in territorial disputes or members of the home pride when fighting at a kill. Crippled lions and cubs may fall victim to hyenas and leopards or be trampled by buffalo or elephants. Careless lions may be maimed when hunting prey. Ticks commonly infest the ears, neck and groin regions of the lions. Adult forms of several tapeworm species of the genus Taenia have been isolated from lion intestines, having been ingested as larvae in antelope meat. Lions in the Ngorongoro Crater were afflicted by an outbreak of stable fly (Stomoxys calcitrans) in 1962, resulting in lions becoming emaciated and covered in bloody, bare patches. Lions sought unsuccessfully to evade the biting flies by climbing trees or crawling into hyena burrows; many died or migrated and the local population dropped from 70 to 15 individuals. A more recent outbreak in 2001 killed six lions. Captive lions have been infected with canine distemper virus (CDV) since at least the mid-1970s. CDV is spread by domestic dogs and other carnivores; a 1994 outbreak in Serengeti National Park resulted in many lions developing neurological symptoms such as seizures. During the outbreak, several lions died from pneumonia and encephalitis. Feline immunodeficiency virus and lentivirus also affect captive lions. Communication When resting, lion socialisation occurs through a number of behaviours; the animal's expressive movements are highly developed. The most common peaceful, tactile gestures are head rubbing and social licking, which have been compared with the role of allogrooming among primates. Head rubbing—nuzzling the forehead, face and neck against another lion—appears to be a form of greeting and is seen often after an animal has been apart from others or after a fight or confrontation. Males tend to rub other males, while cubs and females rub females. Social licking often occurs in tandem with head rubbing; it is generally mutual and the recipient appears to express pleasure. The head and neck are the most common parts of the body licked; this behaviour may have arisen out of utility because lions