Females in oestrus will signal their availability by scent marking more frequently and increasing their vocalisations. Although for the most part avoiding each other, tigers are not always territorial and relationships between individuals can be complex. An adult of either sex will sometimes share its kill with others, even those who may not be related to them. George Schaller observed a male share a kill with two females and four cubs. Unlike male lions, male tigers allow females and cubs to feed on the kill before the male is finished with it; all involved generally seem to behave amicably, in contrast to the competitive behaviour shown by a lion pride. Stephen Mills described a social feeding event in Ranthambhore National Park:  Occasionally, male tigers participate in raising cubs, usually their own, but this is extremely rare and not always well understood. In May 2015, Amur tigers were photographed by camera traps in the Sikhote-Alin Bioshpere Reserve. The photos show a male Amur tiger pass by, followed by a female and three cubs within the span of about two minutes. In Ranthambore, a male Bengal tiger raised and defended two orphaned female cubs after their mother had died of illness. The cubs remained under his care, he supplied them with food, protected them from his rival and sister, and apparently also trained them. Male tigers are generally more intolerant of other males within their territories than females are of other females. Territory disputes are usually solved by displays of intimidation rather than outright aggression. Several such incidents have been observed in which the subordinate tiger yielded defeat by rolling onto its back and showing its belly in a submissive posture. Once dominance has been established, a male may tolerate a subordinate within his range, as long as they do not live in too close quarters. The most aggressive disputes tend to occur between two males when a female is in oestrus, and sometimes resulted in the death of one of the males. Facial expressions include the "defense threat", where an individual bares its teeth, flattens its ears and its pupils enlarge. Both males and females show a flehmen response, a characteristic grimace, when sniffing urine markings, but flehmen is more often associated with males detecting the markings made by tigresses in oestrus. Like other "Panthera", tigers roar, particularly in aggressive situations, during the mating season or when making a kill. There are two different roars: the "true" roar is made using the hyoid apparatus and forced through an open mouth as it progressively closes, and the shorter, harsher "coughing" roar is made with the mouth open and teeth exposed.