The Na'vi are monogamous creatures who mate for life. The mechanics of reproduction are similar to that of humans and other Terran mammals. However, their unique physiology provides the Na'vi with a level of intimacy unknown on Earth. Cultural anthropologists believe that when an appropriate mate has been selected (which can take many years), the male and female Na'vi will connect queues in an act called tsaheylu to create an emotional bond that lasts a lifetime. The intertwining of queues is both highly erotic and profoundly spiritual, but does not in itself lead to reproduction.
Traditionally, once a Na'vi male has passed the tests on the path to manhood and has been accepted into the clan as an adult, he is not only allowed to make his bow from the wood of the Hometree, but he is also expected to choose his woman. After the woman has been chosen, the new couple are mated before Eywa.
Once tsaheylu is made between the couple, the ultimate in intimacy, pleasure that is unfathomable to humans, causes the somewhat unwillful sharing of the couple's good memories, and is a sign of Eywa's acceptance. If a couple can be foreseen to not have a pleasant or happy future, Eywa has been known to reverse the feeling produced by making tsaheylu, a sign to the couple that mating would only, in simple words, ruin their lives together, and therefore prevents the mating, because of its lifelong span. After the resulting embracing and kissing, the couple is sent to sleep by Eywa, and the two dream hintings of their future together. The couple will experience the pleasure of tsaheylu from the moment of connection, until they awaken and have completed mating, and when they disconnect and return to their clan, they are mated for life.