Hagrid shook his head ruefully at the group he was leading through the halls to their first detention with him. He wasn't going to waste time lecturing them, or saying he was disappointed. Honestly, he expected first years to buck the rules a little bit, and he knew Penny was doing more than that without getting in trouble for it. No, the one he was really disappointed in was the one he'd be seeing once they got to work. He knew better, after all. Besides, at least no one had gotten hurt.
Seeing the size of the hole left in the wall, that relief became all the more prominent in his mind, even if he didn't let it show on his face. Instead, he kept a firm, disappointed glower on his face as he locked eyes with the three apologetic faces within that whimpered at him. "None o' that now, Fluffy," he scolded firmly, making the heads droop. "Yer smart enough ta know where you're supposed to be and what yer supposed ta do. I lent ye ta Dumbledore to stand guard, and that's what yer supposed ta do."
Fluffy's right head whimpered and pointed accusingly towards Penny, while the middle head gestured expansively towards all the students Hagrid was leading. The left head drooped apologetically while giving an aggrieved look towards those that shared his shoulders.
"Hogwarts looks after its own, ye know that!" Hagrid insisted to the middle head. "If any o' them actually got seriously hurt, Pomfrey would know about it immediately and send an Elf ta get 'em. Yer supposed to help him keep him in check!" He gestured first to the left head and then to the right as he spoke, resulting in the middle head drooping apologetically. The right head, now realizing it was outvoted, lowered to admit its own malignancy. Sighing, Hagrid walked forward, petting each head in turn. "It's alright, Fluffy," he told all three warmly. "I ain't mad, not really...just disappointed. Ye do better in the future, okay?" All three heads perked up and gave affirmative barks. "That's the spirit!" he praised before turning back to the students. "Now lets get ta work fixin' this hole, hear? Got a lotta work ta do, and ye'll be workin' wit' me each evening till it's fixed. Sooner it's fixed, sooner ya get yer evening's back."
Harry set down the bag of tools while Fred and George set down the bucket of mortar and the bag of stones. Both were much bigger on the inside for the amount of work that would need to be done, and it would need to be done carefully. There was only so much of this particular form of stone available at a time, and any other stone or mortar mix would not mesh with the castle's magic. Thankfully, as long as it was close enough, the castle itself would shift everything into the proper arrangement once the job was done as long as they didn't use any magic in the actual construction work. Doing so would interfere with the castle healing itself.
"His name is Fluffy?" Ron asked in surprise.
"I feel like I should be stunned, but somehow it feels like it makes sense," Penny pointed out nervously, keeping Harry between herself and Fluffy.
"Well, Kerberos - the original Cerberus for which the species is named - translates to 'Spotted', which means he was basically called 'Spot', so..." Hermione allowed thoughtfully, staring up at the beast in fascination. Now that she knew he worked for Hogwarts as a guard dog, she'd lost any fear of an unprovoked attack. As long as she didn't try to get past his post, he'd likely be quite friendly. "Hagrid, do all of Fluffy's species look like this, or do they come in different breeds like non-magical dogs?"
"Oh, they come in breeds," Hagrid assured her with a grin. "Though they don't breed true the way Muggle dogs do. Instead their breed reflects their personality. What the breed they resemble is known for, that's what they're like."
"I see why Dumbledore requested Fluffy then," Penny offered, relaxing somewhat. "He looks like a Rottweiler, and despite their size and apparent viciousness, they're nurse dogs at heart and excellent with children." All three of Fluffy's heads seemed to preen at that assertion.
"Can I pet him?" Neville asked hopefully, getting an eager reaction from the right head.
"Get some work done first," Hagrid insisted. "Otherwise, detention's'll last till Spring, and ye won't get any homework done." He chuckled as Hermione yelped at that, rushing to the bucket of mortar with one of the trowels and immediately starting to spread it. She had a good eye for it, and didn't leave any excess...though she was being a bit too much of a perfectionist. Still, he could leave that task for her, then.
"So what's he guarding?" Fred asked curiously as he hefted one of the stones out of the bag, pausing at the uneven, rough shape.
"Gotta be important if it calls for Fluffy," George pointed out as he looked for a chisel among the tools, confused when he found none.
"Ah ain't tellin' ya that!" Hagrid insisted firmly as he took the stone, casually smoothing it out with his bare hands before handing it to a stunned Harry and Penny to place. It was still big enough it took both of them to place it properly. "It's not yer business!"
"It's whatever you took out of Vault 713 at Gringotts, right?" Harry asked curiously, making Hagrid flinch. "You said you were doing that as a favor to Professor Dumbledore after all, and you lent Fluffy to him to act as a guard."
Hagrid frowned ruefully, not liking that the kids were getting answers, but unable to refute it. "I won't say no, but ah won't say aye either."
"What was it?" Ron asked eagerly.
"Didn't see it," Harry replied as Neville and Ron took the next smoothed stone from Hagrid. At least they had managed to get the entire operation running smoothly, much to Hagrid's pleasure and an impressed Fluffy. "All I saw was a grubby looking package small enough I could have held it in one hand."
"Must be pretty magical, then," Penny pointed out thoughtfully. "Strong enough you wouldn't want to use Fluffy's inner pouch to hide it."
"...inner pouch?" Hermione asked uncertainly.
"Each of a Cerberus' three heads leads to a different set of internals," Penny explained. "The middle head leads to the digestive system, so both other heads can be on watch while eating. The left head leads to a much more intense digestive tract that gets less energy but purges any and all toxins, so it's the head that eats when they aren't certain if food has been tampered with...or if they need to devour an enemy. The right head leads to an internal storage pouch, however, that can only release its contents if the heads choose to do so...but it's not safe to have them store something that has magic stronger than their own."
"Yeah," Hagrid agreed somewhat distractedly. "That's why we didn't use it." In what he hoped was a quiet murmur, he added, "...certainly not cause ah didn't know about that..."
"If it's that magical, Fluffy can't be all that's guarding it," Hermione insisted firmly. "Especially not when he left his post to see to student safety...or to chase a squirrel." Fluffy's heads let out defensive, apologetic whimpers.
"Then the other defenses are likely much more dangerous," Fred concluded thoughtfully.
"And Fluffy's here less to guard the object, and more to keep students away from the rest of the defenses," George added, making Fluffy's heads nod in confirmation.
"Now I want to see what's under that trapdoor!" both twins stated eagerly, making Fluffy growl and Hagrid frown darkly.
"Look, stop askin' about wut's down there!" Hagrid insisted angrily. "It ain't the concern o' students what Hogwarts staff does in areas o' the school students ain't supposed ta be, and anyway, what's bein' guarded is between Albus Dumbledore and Nicholas Flamel, and no one's business but theirs!" Seeing every head - including Fluffy's - swivel to stare at him, Hagrid lowered his eyes sheepishly. "Ah shouldn'a said that..."
"Nicholas Flamel the alchemist?" Penny asked excitedly. "My Uncle Merry introduced me to him! He and his wife are really nice, and they loved talking about everything they've lived through after over 600 years."
"600 years?" Hermione gasped in shock. "How could they possibly have lived that long?"
"Oh, that's easy," Penny explained dismissively. "Nicholas managed his magnum opus of creating a Philosopher's Stone during his first century. While he doesn't use the lead-to-gold effect much to avoid destabilizing the economy due to a glut of the then-no-longer precious metal, it also makes the Elixer of Life which rejuvenates both body and magic when drunk, drastically extending the lifespan in the process while also repairing any damage - physical or magical - the drinker has experienced."
As everyone fell silent, glancing from Penny to Hagrid, Fluffy buried his left and middle faces in his front paws and Hagrid muttered, "I really shouldn'a said that..."