Mark stands up, with the dildo in his hand. "Cal, you should feel my cock in your ass."
Cal's thoughts now change to Cal's canine cock, "You bet." Cal gets up and stands next to the bed, staring at Mark's throbbing pink shaft.
Mark gets on the bed, and pats a spot next to him, "Up here."
Cal climbs on the bed, and lies down on his stomach, his ass in the air. Mark sits up on his knees, and moves over behind Cal, aiming his canine cock into Cal's ass. Soon, Mark slides in and Cal lets out a human grunt. Mark begins to thrust back and forth into his friends ass. Soon, Mark's body tenses, and he fills Cal's ass with his knot while pumping his seed deep inside Cal. Cal squeezes his sphincter around Mark's shaft, amazed that the huge Rottweiler knot is buried in his human ass.
Cal breaths heavily, and says, "Great cock!"
Mark, also enjoying the feeling of his knot inside Cal's ass, says, "And you want this cock all the time."
After a few minutes, Mark's knot shrinks and allows him to slide out of Cal's ass. Call attempts to roll over, and Mark slaps Cal's butt, "I'm not done yet..." and then Mark picks up the dildo. Mark commands, "Cal, take off the collar. And just as Cal pulls the collar off around his neck, Mark slides the dildo into Cal's ass and begins to quickly thrust back and forth in the slick, well lubed ass. Soon, Mark notices a change between Cal's legs.
Cal thrusts his rear into Mark's thrusts, as he grunts "More!"
Mark continues, and watches at Cal's balls shrink and are sucked into a hole, soon absorbing Cal's cock. After a few more moments, Cal erupts in orgasm, a white spooge squirting out of what looks like a small, tight canine vagina.
As Mark pulls the dildo out of Cal, Mark thinks about what he should say. Cal turns over and looks down at what he expects to be a large German Shepard cock, but freezes in disbelief and shock that he no longer has a cock.
"Cal?" asks Mark.
Cal's head slowly rises, a look of surprise slowly turns to a smile.
"Why are you happy?" questions Mark.
Cal gives a hearty laugh, and with a deep breath, "I can have your cock like I wanted to." Cal says as he exhales, pausing for a few moments, lightly touching his new canine pussy, then continuing, "When I had the collar on, my mind was filled with a lust for your cock. I wanted canine cock. The dildo must have done this. It gave you a huge canine cock. I don't know why it did this to me though."
"When you were pumping the dildo, my mind was filled with the feeling of the rottweiler cock between my legs. Maybe the dildo can make what we want, our lustful desires, happen." suggests Mark.
"I'm not sure how we can reverse it" adds Cal.
Mark quickly responds, "I want to stay this way Cal." Mark idly strokes his fuzzy sheath, "I love how this feels."
Cal lays down on his back, spreading his legs. Cal tries to talk in a sultry way, "Well, do you want to see if I can fit you inside me? I am horny as hell, and if the dildo can make me a dog, I have no idea what the limits of it are."
Mark puts down the dildo on a table next to the bed, and then crawls on top of Cal, sliding his recharged cock tip to the entrance of Cal's new pussy, and then slowly pushes in. Cal lets out a scream of pain, "Damn Mark, that shit hurts." As Mark slides deeper, the pain becomes pleasant, as Cal wraps his legs around Mark's butt. No other words are said as both make passionate canine love over and over until both fall asleep, Mark's knot firmly planted inside Cal's now well used pussy.