One day Phineas was planning on what to do for the day when he noticed his very hot platypus pet crawl by "Oh, hey Perry...' he purred seductively' I noticed you're kinda...Hot today" the teen said as he pulled out his unwashed, moldy looking man cannon.
"Yo, what the fuck bro this is sick!" said Perry, though all Phineas heard was an audible squirrel-sounding-like-a-dead-budgie-with-a-windpipe-cleasner-tube purr, he took that as a "fuck me like a hobo fucks a dead, 5 month old black baby" yes.
Phineas quickly grabbed the little green cockslot and shoved is stinky teen boy tool into Perry's unmentionably filled garage, and started to wildly fuck him with such gusto that it's like a gorilla raping his young, and equally as hot to!
He fucked Perry like no tomorrow, with the skin around his cock starting to peel like a blood sausage is sliced open, with pus and blood slithering down the teen's rather pale legs and it matted the fur around Perry's bum, Phineas couldn't take it anymore and turned the little fucktoy around and violently smashed his crotch into the poor fuck's eye socket, tearing masses of skin and bone as it embedded itself in Phineas's cock, every bone and patch of skin bloodying it up even further. Finally he tore Perry's fragile jaw open and came inside his newly formed mouth-ass, he then pissed and shitted inside the animal and went on with his day.
Later he hung the poor fucktoy's pelvis on his fireplace, making sure it goes next to his in-law brother, Ferb's, ribcage.