Argus Filch trudged through the door of his room after a long night of patrolling the hallways of Hogwarts.
"Meow," Mrs. Norris purred seductively as Filch stripped off his clothes.
"Well, well, well! Rawr right back to ya!" Filch said in a gruff voice, beginning to perform pelvic thrusts for his cat's amusement.
And he was naked. Butt naked.
That's not a pretty mental image.
…Think about it.
Mrs. Norris purred again.
Argus climbed into his bed, then slowly prowled toward his cat, grabbing her then pulling her toward his chest. Mrs. Norris licked his skin slowly, thoroughly enjoying the sweaty, dirty, grimy feel of it.
"Mrs. Norris…" Filch whispered deeply, caressing his cat's face then proceeding to kiss it passionately, his hands running through her long, black hair.
Mrs. Norris ran her tongue around the outside of her master's lips, clawing at his chest with her paws. Filch grunted in approval.
"Ahh, Mrs. Norris, you bad kitty." He climbed on top of her. "I would give up my virginity for you."
"Oh, well that's good." A deep voice rang from inside the black cat.
Argus jumped back, eyes wide in shock. "Mrs. Norris?!"
"No," the voice sounded. Mrs. Norris shifted, became larger, then transformed into an actual human being.
"Severus?!"
"Now you've got it," Snape said, sexily ripping open his own robes and throwing himself on top of Filch.
"You—you were Mrs. Norris—all along?!" Argus asked, beginning to hyperventilate.
"Oh, you didn't know my animagus form is a black cat?"
"I didn't know you had an animagus form…"
Snape paused. "Oh. Well…I do. Now…" Severus smirked seductively, "what was that about giving up your virginity?"
Filch gulped and hoped that he would live long enough to see the sun again.