'Back' To Experimenting

Without really listening, Susan calls out "You're going to go back for more?" You could hear a hurt tone in her voice as she looks over to her twin. "Why can't I have the option to be experimented on next?"

"Well my device is fully planned and schematically drawn, is yours?" Mary said with sass. Susan lowers her head in reply, going back to the drawing table. Seeing that, Mary looks at me "But Susan does have a point maybe I should let you experiment with my back entrance!"

All I'm thinking is 'Great I don't even have to mentally tell her!' as I watch Mary roll onto her stomach. Without hesitating I position myself between her legs and gently spread her ass cheeks. Starting with my tongue, lavishing her small puckered brown hole with plenty of saliva. I could hear her giggling as I licked her."That tickles!" she said. I reach over and get a tube of KY jelly to make it easier on her and me. Lathering up both her asshole and my cock, I ask her if she ready.

Nodding her head, I begin to enter her tight hole. I moved super slowly, not even an inch at a time. Yet, Mary still was biting her bottom lip and whimpered slightly as I continue entering her. Finally, I got all of the head into her, "God, Mary I've only got my head inside, still more than half foot to go!"

"You're kidding, right?" Her eyes seemed like the were going to bulge out of there sockets as I start pushing more of my cock inside. Ten minutes later, I finally got it all in her ass, tears flowing down her face as I begin thrusting. Then her cries of pain shatter the air "Oh God, you're tearing my open!" followed by "Ahhhhhhhhh!!!" Susan, who decided to taunt her twin for being so selfish, Said to her twin "Relax! Remember how easy it was to put a pencil up there!"

Five minutes of thrusting is more than enough for her to endure, so I don't hold back. Pulling out until only the tip remains, rubbing my shaft with two fingers, making my cum in her bowels. Gently extracting my cock, a little pop sound then a dribble of cum, from a slowly closing sphincter.

"Oh Susan, trust me, do anal before vaginal!" Mary told her sister happily. "My ass feels like it's able to take Gil's hand with no problem with an ice cube in it to cool the burning sensations!"

"Great advice sis, I'll have to take it up" She winked at me at that. "There is a problem with both our projects though, sis!" coming over to the bed with both schematics, "We need Plutonium to make them feasible in this reality!"

"So lets just go online and order some like we did back home in Porkbelly!"

"I've checked on that sis!" she said, as she held up a iPhone"It says here it a government controlled substance, not for sale to just anyone!" Sighs from both girls as they look to me. "Looks like all we've been doing is learning how to be with Gil!"

"Oh, I don't know about that?" I say