107. Mrs. Norris was a woman… At one point. Back in Filch’s younger days, he had an affair with Mr. Norris’s wife, a muggle, and Mr. Norris found out about it and turned his wife into a cat. A squib himself, Argus couldn’t turn her back, and he refused to bring her to a wizard out of pure shame, so he kept her as a pet. No one ever knew, and the secret died with him.
It’s amazing what pops into your head when you’re walking to the bus stop in -40 degree weather.