The design was illogical, Spock had always thought so. Functional reproductive organs are the single most important facet of longivity among any civilization. Therefore, Spock had always been at something of a loss to discover that so many different humanoid species had not evolved as Vulcans had in this particular area of anatomy.
Furthermore, his own base reaction to the display of such genetalia, specifically that of his own human lover, was thus far inexplicable. Jim had a curious penchant for walking around his cabin in the nude--after a shower, between changing clothes and always after intercourse. Therefore, Spock had found himself with ample time to observe and analyze the human male organs.
Of course, it was less than easy to maintain an objective mind when said organ was actively invovled in the act of fruitless coitus. They would bear no children, and that fact alone should have been enough to avoid such an illogical display, and yet...it was not.
"God, Spock," Jim's voice, low and breathy, brushes against the tip of one Vulcan ear, and Spock's pulse doubles in his side. "So tight..."
Spock risks a glance down to the point where their bodies are joined, his own sex on lewd display where it bounces between their heaving abdomens. It is not an unusual sight to behold--a typical Vulcan male organ, fully extended, two ridges just below the head and wet with fluid--but the sight of it...the feel of it sliding against soft, human skin is altogether overwhelming, and he must look away.
For Jim, whose own phallus is so simple in its make--the foreskin having been cut to display a rounded tip and a single ridge--as it is slowly pulled out and slipped back into Spock's body, over and over in a rythm that he knows is intended to slowly drive him mad with longing, pushes at his control with mounting force. Their differences are so basic, and yet he is lost to them.
Jim, having long known of Spock's obsession with his body, likes to draw it out...his insatiable, alien lover. Likes to enter his body slowly, likes to submerge the thick head of his human cock just enough to...pop...past the first ring of muscle. Spock's body arches for more of its own accord, the intial feeling of being penetrated, of Jim's organ rotating just inside of his entrance and it is nowhere near enough. Until slowly, slowly, slowly, the hard, heated shaft is pushed in...slick and throbbing.
Another curious trick of evolution, heavy and full, Jim's testicles press between his spread cheeks...slapping against him with every thrust as the pace becomes increasingly forceful. It is illogical...that he should find this sight so unbearably arousing...should yearn for it at odd moments in the day...and yet...he cannot get enough.
"Jim," he hears himself utter, as if floating just ouside his own body, watching it writhe and shiver as Jim pushes and pushes, licking and kissing with pink lips and wet tongue.
"Yes," Jim answers, eyes closed and mouth slihtly open, his head thrown back in the same bliss Spock feels with his own flesh.
And Spock is coming, sticky and thick between them, as Jim's eyes snap open to watch, his hips thrashing desperately until finally his back arches in and stiffens with his own release. And now it's Spock's turn to watch and to feel, as he is filled with Jim's essence. It is this sight that he longs to see most...
The human penis softens and slowly slides from his body as Jim rolls to his side and gathers his panting Vulcan to his side--for Spock does belong to this man. It is illogical...
He's always thought so...
But more, it is wholly unregrettable.