SPOCK: No. No. It is not. We shield it with ritual and customs shrouded in antiquity. You humans have no conception. It strips our minds from us. It brings a madness which rips away our veneer of civilization. It is the pon farr. The time of mating. There are precedents in nature, Captain. The giant eelbirds of Regulus Five, once each eleven years they must return to the caverns where they hatched. On your Earth, the salmon. They must return to that one stream where they were born, to spawn or die in trying.