Jeff stared as the tail that held his hand down began to change, thickening and growing even heavier and stronger as it lengthened. It turned black as hard scales began to cover it, beginning at the tip and extending up towards Mike's body. Mike squealed as his hind paws were absorbed into the advancing tail, which stopped just at his hips. A muscular, mutant rat body perched atop a thick, strong coil of a snake. But the scales didn't stop there, continuing up his back as a thin strip down his spine before widening again into a recognisable cobra hood, overshadowing his otherwise rat-like face. Mike's squeaks became hisses as his tongue forked, growing long and black, and two hooked fangs dropped from the roof of his mouth.
Satisfied, Mike let Jeff go, stopping his transformation to get a look at his body. It was certainly intimidating. His front half had grown slightly, becoming a whole foot of rattish parody of a bodybuilder, his soccer ball biceps and brickwork abs still just as chiselled as ever. Then, behind him, three more feet of snake tail, thick as Jeff's waist, extending down in mountains of coils to a whip-thin end. Mike raised himself, now half Jeff's 6-foot height atop his tail, and bared his venomous fangs, hissing in delight.
"Yeah, very cool, Dad," Jeff muttered, a little nervous. He could feel coils wrapping around his feet as his dad swayed closer. "Hey, can you let me go?"
Mike hissed, a parody of a laugh. His tail began to wrap higher around Jeff's legs, and he used the leverage to bring himself eye-to-eye with his son. He pressed his forehead against Jeff's, flaring his hood and staring deeply into his gaze. His tongue flickered out, licking gently across Jeff's upper lip, giving Mike a good taste of his salty sweat. He lapped every speck up eagerly.
Against the exposed skin of his collarbone, Jeff could feel something moving, something stirring. There was a slight pressure, one bump, then a second pushing against him. With each second, he could feel Mike's heartbeat through them, throbbing in time as the bumps grew larger. Barbs tickled against his skin. "Dad, what's going on?"
Mike didn't answer, eyes rolling back in his head as he let out a deep, hissing moan and lifted his body. Jeff looked down. There, were two stiffening snake cocks.