The wizard stepped carefully into the chamber. Something otherwordly was definitely occuring - the contents and furniture of the room were scattered chaotically all about. Many things were still hovering to and fro, and an ethereal moan shuddered through the air.
"So what is it, master wizard?" the chamberlain asked tremulously. "A poltergeist?"
The wizard stroked his long, greying beard thoughtfully, briefly leaning to one side as a flagon hurled itself in his direction. "Maybe..." he pondered as the dented drinking vessel rolled away.
"Then again, maybe not. This haunting doesn't quite... taste right, so to speak. It feels somehow different to a poltergeist's work."
"W-well, is there anything we can do?"
"To begin, we need to ascertain the exact nature of this entity. Luckily, I have the correct instrument..."
The wizard reached into his robe and pulled out an odd glass cuboid, bound in an ornate brass frame. The interior of the vessel was full of a purplish fog, billowing and roiling to itself.
The chamberlain stared at the gas curiously. "What's that?"
"A simple experiment. Watch..."
The wizard held the glass cuboid out before him, hanging from a thin chain. Almost immediately, the purple miasma separated into red and blue, each colour neatly sequestering itself into one half of the vessel.
"Just as I suspected - a demon."

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Something I came up with in the bath. If you don't get it, it's a science joke.