I live in a basement flat. When I returned home from work this evening, I noticed that at the bottom of the stairs, in the hallway, on the wooden floor, there was a wet patch - about the size of a dinner plate.

Mrs HYG was in the living room - she'd been home for about half an hour. I asked her if she'd spilt something in the hall. She asked what I was talking about, and I told her there was a wet patch on the floor. She came to look at it, and insisted it hadn't been there when she got home, and she hadn't spilt something.

Slightly confused but too tired to make a fuss, I got some paper towels and mopped it up - which is when the story takes a strange, and disgusting, twist. Judging from the smell and colour, this wasn't just water on the floor. It was piss.

I looked at the ceiling above the wet patch, and nothing seems untoward. There is a light fitting with a bare bulb above the spot (though maybe a foot or so away from the patch exactly), but it was dry - no drips or anything. I can't tell if the ceiling as a whole has any damp patches - it's an old flat, and the paint is fairly faded. There could be, but nothing obvious. Directly above it either the entry hall to the building or the stairs to the top floor flat, not a bathroom / kitchen, though there may be a pipe.

The other thing which came to mind was an animal. We don't have pets, but could an animal have come in and pissed on the floor? Seems unlikely. I checked the flat on the tiny chance a cat had got in and hidden itself away, but found nothing. I guess it could be a mice, or a rat, but it seems like a lot of piss for a small animal.

So, what the fuck has happened? In the several hours I've been home, no more piss has appeared.

a) Mrs HYG is fucking with me
b) Mrs HYG had a weird blackout, pissed on the floor, and forgot about it
c) There is a leak from above
d) An mysterious animal pissed there
e) Ghosts

I'm expecting comedy replies here, but honestly, any actual guesses would be appreciated, I'm slightly freaked out.