I am so small now that he doesn't even feel me fall through his piss slit. I am expecting to take over his body but don't know how or what I have to do. Inside his cock I travel upward but the walls around me are moving as he gets hard and his cock swells in size. Some precum is flowing past me pushing me towards the opening. I better hurry or else I'll be outside for good on the shower wall or worse in Doogies ass. Hmmm. I sprint up his cock and make it to where his balls are. This must be the point where I take him. His balls start shaking violently. He must be fucking the doc. I can't stay here and I fall head first into his right nut. My body swells bigger as it absorbs all the fluids around me. I'm now pushing out the sides of his ball and the movement stops. I hear him say, "FUCK", and the next second his hand surrounds me and I am looking out of his eyes at the face of Doogie. "OH YEAH", I yell out of his now my mouth. Doogie doesn't know what's going on as I am feeling all of my new body which is absolutely incredible.. Doogie gives me an inquisitive look so I tell him to "Just hang on a minute". It's time for me to test out my new power. With my massive cock up his butt I begin to take in all of his size and as a bonus I can have his knowledge also. His screams are muffled my my stupendous chest as he slowly shrinks and all of his mass comes into me. My arms have to be over sixty inches but they are in perfect proportion with the rest of me. My cock is pushing out of his body as he shrinks around it. I don't want to kill him so I pop him off and hold him up in my right hand. "So Doc, seems the experiment was a HUGE success if I must say so. Thanks for the size and knowledge. I now know all about your experiments and what works and what doesn't. If you're a good little man maybe I'll do some experimenting on you."