Spock sat at his science console, thinking about Jim Kirk's balls.
Of course, he was also thinking about the Enterprise's current mission, the condition of the scientific devices in front of him, his pet mathematical equation of the moment, and ensuring his facial expression was calm and level. But chief on his mind was the pretty sac between his captain's legs.
It was not a particularly large set of balls, from what he understood of human averages, nor small either. Jim kept them hairless for his own comfort and for Spock's convenience--much like the rest of his body--and they were indeed most enjoyable to handle.
They were deceptively vulnerable and delicate for something that held so much power inside. The slightest caress there would make Jim smile and liquefy. Spock was glad that this was so easy to accomplish, as he was relatively unpracticed in the arts of love. The skin there was soft and pleasurable to his fingers, which, since he was a Vulcan, were far more sensitive than the fingers of a human and could appreciate the eroticism of the texture much more thoroughly.
Spock's fingers now scurried over the controls of his science panel as he smugly processed the thought that he was glad his Vulcan training allowed him to think such inappropriate thoughts in public without any of his coworkers being the wiser.
He remembered fondly the way the pliant skin of Jim's balls practically nestled up to his tongue when he approached them. He was very careful with them, and gave them lots of devoted attention. Jim rewarded him with a host of noises that would have reduced the Martian polar ice caps to a steaming ocean of desire. The captain definitely enjoyed having his balls licked.
Spock liked Jim's penis, too, of course, but he could think about that later. Right now he was in the mood for Jim's testicles, lying against Jim's thigh in luxurious repose, or filling up his own mouth as he performed the act known as 'tea-bagging'. On Vulcan, tea was always brewed loose-leaf, so it had taken Spock a short excursion through the ship's computer to learn just why enveloping a man's balls in one's mouth had been given that nickname.
Of course, in that case, the 'tea' with which one was rewarded was mostly cream. Spock turned up his Vulcan control a notch to mask his amusement at his own naughty joke.
He turned slightly in order to gather a glimpse of his beloved with the corner of his eye. Jim was on his perch in the captain's seat, talking to McCoy. He seemed to subconsciously sense that Spock was now watching him, and shifted seductively in his chair. Spock could almost barely discern the outline of an appealing bulge in Jim's tight uniform pants. Keeping one eye carefully fixed on his viewfinder, he used the other to memorize the tantalizing sight.
McCoy had finished talking to Kirk and stepped up a level to bother Spock. "Whatcha lookin' at, Spock? Stargazin'?"
"I am studying globular clusters," Spock found himself saying. The tips of his ears burned as if they'd been pinched.
McCoy walked away, suitably bored with Spock's monotone answer.
Spock returned to his work, happily daydreaming of Jim's stellar spheres, and the outpouring of stars preserved within.