A testicle

"All I want is a testicle, Sweetie," River tells you. "That's all, just one. The left one."

You look at her askance.

"Oh, be reasonable," she says. "You've got two, and they'll cause you nothing but pain." She starts to look at the console, her fingers running lightly over the buttons with the names on. "All I have to do is press one of these and whoever turns up will want to own your balls. They might play with them, leaving them as blue as the Tardis, or punish them, leaving them black as well as blue. They might just remove both of them, and maybe your cock too. I'm being very reasonable here."

You notice your hands are cupping your balls, you're clearly not eager to dispose of either of them. Then River's hand is on your hands.

"There there, Sweetie, I realize you're attached to them, but there's still things you can do with one ball - have mind-blowing sex, father children, initiate world wars. Maybe we can do them all today, and then we can do Amy. You think about it."

Her hand pulls at your hand, and reluctantly you move it and your other hand aside, letting her rub your balls before moving to your cock.

"We both know you're going to give me what I want," she says, as her hand strokes your cock, and you stare into her deep blue-grey-green eyes. "I know because..." her hand speeds up, stimulating your cock, ".. I've met you before..." her grip tightens, "... in your future..." her hand's working you, taking you to the edge, "...though I didn't recognize you straight away because..." You feel your cock getting ready to explode. "Spoilers, Sweetie," she says, letting go of your cock, leaving you frustrated as it bobs about, sperm dripping out of it.

"Oh, did I ruin it for you?" she says innocently. "Well, maybe if you wanted me to take away that testicle of yours, I'd let you say a proper goodbye to it, drain it fully before I became its new owner."

She pushes her body towards you, her firm breasts pressing against you.

"So, Sweetie, will you give me that one little thing I crave?"