Wait, since Chloe's theory was a TVTropes reference (see pedanterrific's comment) could the vrooping thing be too?

Oh my Bayes, it's completely obvious:

Clearly visible from where Harry had perched himself on his chair's arm was a truncated-conical object, like a cone with its top snipped off, slowly spinning around a pulsating central light which it shaded but did not obscure.

It's a lampshade. But what was Eliezer lampshading?

ETA: Obvious in retrospect, I should say. Which doesn't actually mean obvious at all.