Test River's reactions

"I'd like to test your physical reactions by fucking you, River."

"What are the parameters of your test?" She has a blank look on her face.

"Doggy-style, I think."

"What does a canine have to do with physical reactions, sir?" She is puzzled.

You think a second and say, "It relates to the position the woman is in. Last night, when Kaylee and later you were on top of me while we fucked, that was called Cowgirl, since you straddled me like riding a horse. Doggy-style is when the woman in on her hands and knees, and the man fucks her from behind. Kind of like when dogs fuck."

"I have never seen canines or cowgirls fucking. Are those the only positions?" River asks as she gets on all fours and presents her ass in the air. Her tight butt is so sexy.

You crawl behind her and say, "No, there are hundreds of positions." Then you slide your cock between her legs, dragging the head across her pussy lips several times.

"That action produces fascinating nerve stimulation. Do that some more. I need to study it."

"Study this, bitch!" you say as you shift your cock and slip straight into River's well-lubricated slit. You grunt as you pull back hard on her hips and thrust forward. You bury your shaft to the hilt inside River's tight cunt. She gasps involuntarily. You immediately start pounding into her rapidly. Her analytical talk has you really turned on for some reason.

River says, pausing each time you strike bottom in her pussy, "That changes ... the parameters ... completely ... from the cowgirl ... position." She paused to catch her breath. "I will in- ... interpolate ... this new data." An unladylike grunt escapes her throat. "Ah! ... Bitch! ... A female ... Unh! ... dog!"

Just as with the blowjob, you start imagining your all-time favorite times fucking a woman from behind, focusing especially on what the woman did that was good. Right on schedule, the psychic girl started pushing her ass back toward you as you thrust into her. Every time you hit bottom inside her, she grunts.