"Mr. Potter, do you intentionally ignore directions or have you been hit too many times by those infernal bludgers?"
Harry yowled angrily and clawed fingers batted in the direction of the irate potions master. Large, black-furred ears plastered against his skull and a long, black tail twitched erratically. "It's not as if I did this on purpose!"
Severus Snape brought a hand to one temple. Albus didn't pay him enough to deal with this. He cursed Minerva for getting the stomach flu in the middle of Potter's animagus lessons and forcing the responsibility of teaching the moron onto him. In front of him, kneading an antique, very expensive seat cushion, was the boy-who-lived-turned-cat. At least, that was what he was supposed to be. Really, he was half and half at this point.
Potter had obviously rushed his training. His fingers (and toes, Severus suspected) were clawed much like a house cat's, large furry ears sat atop his head (his human ears were currently missing), and a tail waved behind him like some sort of insane banner. The boy's eyes hadn't changed color, but Severus thought the pupils looked a little narrow. Human canines had thinned and pointed into cat incisors, his nose had shrunk a bit, and long whiskers jutted out from his cheeks.
Severus sighed and snapped his fingers. The boy stopped batting at the dried specimen on his desk and looked up at him, a snarl on his lips. "Come along, Potter. Poppy will no doubt be pleased you have managed to, once again, get yourself into trouble within a week of leaving her clutches." Potter blanched and Snape felt a rush of sadistic glee. "The only way to reverse your blunder is to drink a potion with the same properties as finite incantatum to flush out the effects of a botched human transfiguration. To put it's taste into perspective for you, it tastes four times as bad as a polyjuice potion." Snape smirked at the look of disgust and horror on Potter's face. "Not that you'd ever tasted the polyjuice potion, right?"
This has been sitting on my computer for far too long, gathering dust. I decided to make my own, admittedly small, contribution to the cat!harry universe.