One of the great things about lions is their collegiality. The family groups have a wonderful sense of companionship. This is perhaps best exemplified among the adolescents. They are similar in many ways to another gregarious mammal, Homo Sapiens.
Teenagers enjoy hanging around together. Sometimes they play fight, sometimes they just lounge and other times they join in some challenge to test their metal. Young lions might tackle a warthog, or try to access a tortoise for example. In this case they have heard a sound and viewed a shape moving behind the bushes, just a dash away. When they see that the shape is a black rhino they realize that any hope of a successful attack, even by three, brave, young lions is only a passing fancy.