He had been thinking about the Christmas event since the morning after Halloween.
Not because he had planned it that way — the timing had been determined by the fact that Halloween had produced The Witness as an identity and The Witness, having been established, required maintenance. A single event was a mystery. Two events were a tradition. He had understood this from the first morning the cards had been on the notice boards, from the moment he had raised his pumpkin juice at Dumbledore and Dumbledore had raised his goblet back.
The castle had been given something. The castle was going to expect more. He was going to give it more.
The question had been: what.
The Halloween event had been beautiful and strange and historically specific — the specific register of something that had treated its audience as people who deserved to be given something real and particular. He was not going to repeat it. The Christmas prank needed to be different in character. Not because Halloween had been the wrong approach — it had been exactly the right approach for Halloween. But Christmas was a different occasion, and the occasions he had thought about most carefully since September were the ones where the response to a large thing had failed to match the character of the thing itself.
Halloween required reverence. Christmas required something else.
He had arrived at the answer on a Tuesday evening in the second week of December, in the specific way that answers arrived when you had been not-thinking about a problem long enough that your subconscious had finished its work and was ready to report back. He had been making a second dashi — more confident now, the temperature management intuitive in the way that things became intuitive after the fifth repetition — and the older elf had been at the far end of the kitchen when the answer arrived, and it had arrived complete, which was always a good sign.
The suits of armour.
Hogwarts had forty-seven suits of armour. He had counted them in October during a late-night walk when he was working off the restlessness of a difficult day, and had noted them in the way he noted everything — with the attention of someone who catalogued what was around him because he did not know in advance what would be useful. Forty-seven suits of armour, distributed across the castle's corridors and staircases and great halls, each one standing in the specific patient stillness of something that had been standing in that specific spot for a very long time and had developed no anxieties about it.
The suits of armour could sing.
He had read this in Hogwarts: A History — a footnote in the chapter on the castle's enchanted fixtures, noting that the armour had been briefly animated during the 1612 Goblin Rebellion to assist in the castle's defense, and that the enchantment had been modified in the following century to include a choral function for ceremonial occasions. The choral enchantment had fallen out of use sometime in the 1800s, had never been formally removed, and remained technically active though no one had triggered it in living memory.
He spent three evenings in the library finding the activation sequence. It was in a footnote of a footnote, in a text from 1743 that had the specific dusty confidence of something that had not been read in its intended context for approximately two hundred years. The sequence was runic — of course it was runic, everything in this castle that was not actively maintained had been built on runes — and it was not complicated, which was either because the original enchanter had been very good or because choir conductors in 1743 had needed to activate it quickly and had designed accordingly.
He read the sequence and thought about the character of the occasion and felt the specific quiet pleasure of something fitting.
The second component was the absurdist element, which he had thought about more carefully than the singing. The singing alone was ceremonial. He did not want ceremonial. He wanted something that was both fully committed and fully ridiculous, that treated its own absurdity seriously, that produced laughter from people who had also been moved and who found the combination unexpected.
He needed a song.
The song he chose took him forty-five minutes of genuine deliberation, which was longer than he usually spent on anything that was not the Ravenclaw book or the compound runic grammar. He went through his mental catalogue of everything he had ever encountered that was simultaneously very seriously performed and objectively ridiculous, and arrived, at the end of forty-five minutes, at a conclusion that was so completely correct that he sat with it for a moment in simple satisfaction before writing it down.