Disclaimer: I don't own Harry Potter (duh).
Neville walked quickly up the stairs to the Gryffindor tower, clutching his list of passwords in his hand. But just as he approached the sleeping Fat Lady's portrait, he saw a dark figure out of the corner of his eye. He turned to see that it was a large dog, staring right at him.
Neville yelped and jumped up, dropping the list on the ground. He had heard about this dog. It was the Grim.
"Back!" he said, fumbling for his wand. "Stay back!"
The dog tilted his head to the side and widened his eyes.
Of course, Neville thought. It's a dog, it doesn't understand about wands. It thinks this is just a stick and I want him to fetch it.
But of course he couldn't do without his wand, not when there was a killer on the loose. He reached into his pocket and grabbed the first thing he could find - his Remembrall. The dog began to pant and wag his tail excitedly.
"You want this?" he said, holding the ball for the dog to see. "Go fetch!"
Neville threw the Remembrall towards the dog. Although it was made of glass, it didn't smash when it hit the stone floor; being magic, it just rolled like a normal ball. Neville had planned to grab the list and make it into the common room while the dog was distracted by the ball. But instead, the dog ran towards Neville and picked up the list in his mouth, running away.
"No! Bad dog!" Neville shouted, running after him. "Give that back! I need it!" He was grateful that he was alone and no one was around to see this embarrassing sight.
As the Remembrall bounced down the stairs, forgotten by both boy and dog, Neville chased the dog down the hall, desperately trying to get his list back. Then suddenly he remembered his wand. He took it out, pointed it at the list, and said "Accio list!"
The paper flew out of the dog's mouth and into Neville's hand. It was covered in drool and he could barely read it. The dog whimpered and looked at Neville's wand.
"No, I'm not going to throw you my wand," Neville said. Then, looking at his wand, he realized that he could fix the damage the dog had done. "Scourgify," he said, pointing his wand at the paper. After a few tries, the drool disappeared and the list was legible again.
The dog whimpered again. Neville looked down and saw that he was lying on his side, his belly turned towards him.
"You want me to give you a belly rub?" Neville asked. The dog panted excitedly.
Neville knelt down and began to pet the dog's belly. He wondered if he was doing it right. The only pet he'd ever had was Trevor, and you didn't pet a toad. But the dog seemed to be enjoying himself. He rolled over so Neville could pet his back and behind his ears.
"I don't know why they call you the Grim," he said. "You're a nice dog. It's not your fault. Just because you're big and black…"
Suddenly the dog licked Neville's face. Neville wiped off the spit and laughed.
"Maybe I should ask Gran to get me a dog," said Neville. "You seem to understand me. Do you know if dogs eat toads?"
Neville could swear that the dog shook his head.
"You mean they don't, or you don't know?"
The dog gestured towards himself with his paw, then shook his head again.
"Oh, so you don't eat toads. That's good." The dog nodded. "Do you have a home? Maybe I could adopt you. What are you doing here at Hogwarts, anyway?"
The dog looked down at the list, then up at the portrait of the Fat Lady.
"You want to get into the Gryffindor common room? Well, I'm sorry, but I'm not allowed to let anyone else in there unless they're a Gryffindor student. And you're not a student at all."
Suddenly the dog stared at something behind him and bolted down the hall. Neville froze, thinking it must be Sirius Black. He raised his wand and prepared for a fight.
"Longbottom? Is that you? Who are you talking to?"
Neville turned around to see McGonagall coming down the hall, her wand illuminated. He breathed a sigh of relief and lowered his wand.
"N-no one," said Neville. He didn't know why he had lied, if he had been trying to protect the dog or simply thought the truth was embarrassing.
"I found this at the base of the stairs," she said, taking his Remembrall out of her bag.
"Oh," he said, taking it back. "Thank you."
"What are you doing over here?"
"Nothing."
"You didn't lose your list of passwords again, did you?"
He shook his head. "It's right here," he said, showing it to her.
"Good," she said. "Now get to bed, Longbottom. Lingering in the hallways alone at night while Sirius Black is on the loose is very unwise."
"Yes, mum." As McGonagall left and headed to her office, Neville went over to the Fat Lady's portrait and woke her up so he could say the password and get inside. As he went in, he looked down the hall one last time to see if the dog was still there. He thought he could see a pair of glowing eyes poking out from behind the wall, but that was it.
Neville lay down on his bed and started thinking about the dog. Why had it run away from McGonagall? Had it thought she was Sirius Black? Would Black try to kill it if he found it? After all, if he cared so little about human life, he'd care even less about animal life. Neville just hoped the dog had enough sense not to bark if it saw Black.