An object materialised, a material fact - which is to say it was presented; but it didn't fit at all with the surrounds, grated on the nerves, made people uneasy, and so some hand must have pressed some lever, a trapdoor shot open, and away slid the fact, down, gone, disappeared, forgotten.
But can a material fact be forgotten just like that? especially such an irritating one. Surely it leaves behind a residue, a shadow.
But apparently it didn't even have to be forgotten, it simply wasn't ever remembered. Noone brought it up. It slipped from the mind as easily as it slipped from the room - so far as one could tell. Mind and room as one, what didn't remain in one didn't remain in the other.