"Dammit Frisky!" Joel shouted as he pulled the syringe out and looked at it. Half the fluid was gone.
"What the fuck Joel, what did you just inject in me!" Stan said rubbing his arm, "I feel light headed."
"here sit on the bed, it should pass in a minute." Joel said watching his brother and wondering what would happen.
"damn its hot." Stan pulled his shirt off. His skin was glistening with sweat and Joel's eyes went wide as he saw cuts of muscle beginning to form on his brothers chest.
Stan looked down just as soft brown hairs began to push out in the middle of his chest. "What did you do to me Joel, I don't even have brown hair." Stan said in a voice that was changing as he spoke. "What's wrong with my voice!"
Joel just starred at him as he watched his brothers blond hair darken to brown and Stan's face change into an older version of his face.
Stan was scared by the look on his brothers face and quickly got up and ran to the mirror on the door. "Holy shit! I look like you, but hairier." He said as the hair on his chest thickened.
"AHHH it itches!" Stan scratched at the crotch of his jeans and ass before unbuttoning them and dropping them and his underwear. His legs were now covered in strait brown hairs and his cock was growing. "What the fuck is wrong with your cock dude?" Stan said as they watched the head grow to a slight point and the base bulged outward. As the skin thinned and turned red Stan screamed, "I have the dog's dick!"
Both were speechless as they watched Stan's continued changes. Fur grew on his face as his tongue grew a little and his face pushed forward slightly. His cock pulled into a sheath as his ears grew fur and expanded an inch upward. Fingers shortened as his nails turned black. Watching his ass as it covered with fur a foot long tail grew out above it, followed by a thin layer of fur covering his back.
Standing there was A more muscled version of Joel's body, what Joel originally wanted with the serum, but because of the dog's DNA, now had some canine features.
Stan looked sternly at Joel before reacting to his new body...