This time six tiles in a row were coming loose. I thought it would be a simple matter of letting the tiles fall off gracefully, scraping off the old sticky, applying some new sticky, and repositioning the tiles. Same as last time but a bit more comprehensive (and hopefully without sticking screwdrivers in my hands -- never let it be said that I don't learn from my stupid mistakes).
All seemed to be going fine until the last tile in the row, behind which lurked Screaming Horrors. I mean, seriously, what on earth is going on behind that last tile? There's a sort of open box (the white bit) at the back of the space; the two dark struts appear to be made of wood, and when poked slightly with a screwdriver the left one wobbles like a loose tooth. Why would you have that behind some bathroom tiles? Is our house actually made of bits of cardboard held together with duct tape?
Should I hide something interesting in there so that the next person who does this gets a more pleasant surprise?
[ETA: don't know why the flickr tags link isn't working for anybody except me, but this should give the idea...]