Thanks guys. They're supposed to make you stop and think 'What the...' for a second until it clicks.
I didn't do anything fancy with these. I just took pictures of reflections in the puddles on the paving. The way I shot them avoided having me in the photo, but left the main subject upside down, so I just rotated them 180 degrees.
Another photographer was watching me for a couple of minutes, probably wondering why I was taking all those boring shots of the ground, and then he lifted his camera and started doing the same. I think he finally realized what I was on about.
Here are a couple more.
And here's an unrotated and uncropped shot which gives the game away.