"Mad! He's a genius!" objects Percy. "Best wizard in the world! ... Well, he is a bit mad, yes. Potatoes?"

Indeed, there are potatoes: for between one eyeblink and the next, the tables have gone from empty to laden with more food, both in variety and in sheer volume, than Bruce has ever seen in one place in his entire life. Most of it is classic savory British fare (assorted roast creatures, sausages, vegetables, gravy, several kinds of potatoes, that sort of thing), except for the pumpkin juice, which is kind of weird, and the peppermint humbugs, which are not that weird aside from their total lack of conspecificity with anything else on the table.

"Woah! Wait, I thought you couldn't make food by magic; where'd it all come from?" (This confusion is decidedly insufficient to prevent him from loading up a plate and tucking in.)

"It gets Apparated in from the kitchen, I believe."

"That's really cool. It's a lot faster than everybody waiting in line for it." 

Ron starts up a conversation with the twins about this year's Quidditch season. Apparently the Gryffindor seeker position is wide open with a field of deeply mediocre potentials and it's all down to who improved their skills most over the summer.

There is a certain degree of periodically elbowing Percy and giggling throughout this conversation; Percy is trying very hard, and somewhat sulkily, not to have an opinion on this, but apparently they've got a bet going with Angelina Johnson on whether Oliver will successfully get him onto a broom before or after Halloween. It is evidently understood to be a possibility not worth even mentioning that Percy will not eventually be conscripted. 

The remainder of the feast passes pleasantly with food and social introductions, and then more food, and then Dumbledore, again, rises to his feet. "Ahem," he says, "just a few more words now that we are all fed and watered. I have a few start-of-term notices to give you. First years should note that the forest on the grounds is forbidden to all pupils. And a few of our older students would do well to remember that as well."

Certainly they are the picture of innocence and cannot possibly be the target of this baseless implication. :) :)

"I have also been asked by Mr. Filch, the caretaker, to remind you all that no magic should be used between classes in the corridors. Quidditch trials will be held in the second week of the term. Anyone interested in playing for their house teams should contact Madam Hooch. And finally, I must tell you that this year, the third-floor corridor on the right-hand side is out of bounds to everyone who does not wish to die a very painful death."

"Painful death? Wait, what does he mean the right-hand side, whose right?"

"The third floor doesn't have north and south. It has widdershins and clockwise."

"The right side is where you get if you've gone down four main hallways in a row making only right turns--"

"left is the opposite of that--"

"and before you've done either you're in the middle."

"Simple really."

"Oh. It's that kind of impossible to map. Thank you."

"Wait, but how did you know that? Is this all purely oral history?? Surely if you can say a whole understandable sentence describing it you could also write it down - "

Dumbledore has no comment on the behavior of the building at this time. He proceeds immediately to conjuring magical floating lyrics and encouraging everyone to sing The School Song.

"Everyone pick their favorite tune, and away we go!"

Hermione did not know about this and she is displeased.

Bruce sings for like a line and a half but he's too distracted by thinking about how you would map the third floor situation with only muggle pencils and paper to keep going when everyone else is going different speeds. You probably want some sort of map-projection-type situation where the important thing to preserve is which locations are next to each other rather than the hallways being straight/curved/parallel/perpendicular/etc. Since the goal here would be to not get lost rather than to guide construction or repairs or whatever. 

Ron sings at a tune and speed as different as possible from the way the twins are singing, which turns out to be "fast and jaunty," which is great because that's how he's feeling right now aside from the "painful death" bit.

Hermione, unable to not follow direct instructions from Dumbledore and also fully unqualified to make up her own tune, attempts to sing along with Ron, somewhat poorly. She's also thinking about the mapping question, but mostly from a perspective of whether, perhaps, someone might have done an analytical survey of all the instructions people pass down student-to-student and written it down and put it in the library. That seems like the sort of thing that someone must have at some point thought to do, if you have the sort of academic institutions that have libraries at all. Right? ... Right? 

When the last strains of the twins' funeral dirge die away, and Dumbledore has finished clapping with great enthusiasm (and the rest of the teachers clapping with somewhat less enthusiasm), that's the end of the feast. "Ah, music. A magic beyond all we do here! And now, bedtime. Off you trot!"

Is there magic music? That probably wasn't a literal assertion but also there probably is magic music. Bruce follows Percy and the other prefects up the stairs, on the lookout for any other magical architecture. 

They take a relatively euclidean route upstairs . . . and upstairs . . . and up some more stairs. At one point they wait for a staircase to swing around to point to a different place, stone flowing and squishing in a way even clay generally can't. There are portraits on the walls whose eyes follow them as they move, and so do their heads, and some of them point and mutter to each other, mostly about how it's nice when the students come back every fall to liven up the place but some about how they prefer the peace and quiet of the summer.

"Are the portraits people?" Bruce whispers to Hermione.

"Hogwarts, A History says there's more magical portraits here than anywhere else in the world, over a thousand, and Modern Magical History talks a lot about recent advancements in painting techniques - in the 1830s, apparently for wizards that's recently, can you imagine - they don't really take an explicit philosophical stance, we'll have to see if we can find somebody who does - anyway probably not? There's this interview in Modern Magical History with the grand-nephew of this fellow Tobias Misslethorpe who's one of the newer portraits, and they obviously don't think it's still him, they talk about how it's 'comforting' and 'a nice reminder' and so on like having a recording of your dead grandpa on your answering machine."

"Huh. Seems--weird but not in a worrying way? We should read about ghosts too; they might be the same kind of thing."