Grudger watched the feline sat on the desk with steady focus.

It watched him in return, its posture stiff and unflinching. Eyes sharp.

Grudger had never seen a human change shape before.

He wondered what else she could turn into.

For now, the small sleek creature with the pointed ears and long tail was all he had seen her become. She felt different like this. Her emotions not quite as intense as they were in the human form. It was quite pleasant.

He felt around for fears. He didn't really want to scare the human. He had grown to like her in the time he and Gretta had been staying in her rooms. But as a boggart he had always learned to look for fears first, it was an instinct of survival.

He found one. A shape that caused a thrum of caution to pass through the cat-human.

He let himself shift.

Growing his own set of ears and a shorter tail.

Large padded feet flexed on the ground. Sharp teeth bared in a low growl.

The felines fur bristled, tail swishing in warning as she stood up, lips drawing back to release an angry hiss.

Beneath the fear Grudger felt a prickle of that same anticipation-fun-excitement which had made him so fond of the younger humans.

He braced his back paws against the stone floor and hoped he was reading her correctly as with a burst of every he sprang forward.

The Transfiguration teacher launched herself from the desk with a piercing yowl and headed for the door, the boggart in close pursuit. Thankfully it was after curfew and most of the castle was asleep so there was no one to interrupt the chase, or misinterpret the situation as one of actual danger.

Somewhere around the fourth floor Mrs Norris caught sight of the snarling creature chasing the cat-human and was sent fleeing back to the safety of Mr Filch, not at all amused by the dog-beast as her almost feline counterpart seemed to be.

For an hour they darted up and down the stairs, in and out of rooms, along ledges and through every nook and cranny they could find, exhilaration vibrating through both human and boggart. Paintings in the hallways watched in confusion as cat and dog prowled the castle halls in a fast-paced chase.

By the end of the game Minerva was rather proud of herself. She hadn't moved like that in years.