At this point the being sprung from human genes shaped by Martian thought, and who could never be either one, completed one stage of his growth, burst out and ceased to be a nestling.  The solitary loneliness of predestined free will was then his and with it the Martian serenity to embrace it, cherish it, savour its bitterness, and accept its consequences.  With tragic joy he knew that this cusp was his, not Jill's.  His water brother could teach, admonish, guide - but choice at a cusp was not shared.  Here was "ownership" beyond any possible sale, gift, hypothecation; owner and owned grokked fully, inseparable. He eternally was the action he had taken at cusp.