There's a ghost in the loo

It's late night, and the office is nearly empty and deathly quiet except for a faraway clickety-clack of the keyboard and faint Dire Straits. Half the lights have been switched off. There's generally a dark, gloomy feel, and because there's no warm bodies, the air is icy cold.
No warm bodies. Damn. Why did I put that thought in my head?

I'm standing in front of the cold porcelain of the urinal, doing my thing, when a drift of cold air sweeps across the back of my neck.
Silence
The stall next to me, which was empty all this while, suddenly flushes in a shocking explosion of hisses and gurgles.
Nobody was there. Nobody's in the toilet. Nobody's in the frickin' office but me!