Headmaster's sound-blocking barrier had no physical manifestation. It just… was.
That is, it continued to exist as this weird sense of blur separating everything on the inside from all of those on the outside… until it didn't.
There was no cinematic collapsing of it, just the fading of the cause that brought forth the desired effect.
"Welcome, everyone," the headmaster boomed as he sat back down on his throne, finally stuck in the very last apparition Theo saw him as.
Or, judging by the apparition's nature, saw her as.
"I apologize for the slight delay, but as you all must be keenly aware, this is a rather extraordinary day, one that warrants extraordinary measures."
Upon sitting down, the headmaster - headmistress? - pulled one of her long legs over the other, while magically making sure for her long, elegant and perfectly modest skirt to keep all the necessary parts hidden away, regardless of what angle one would look at her from.
