A friend decided to take down the internal downstairs chimney breast, he had no concerns as the upstairs bit and chimney had already been removed. He stripped the plaster the remove a couple of bricks from ceiling level, just out of curiosity he got a torch and had a look at the gap between ceiling and upstairs floor.
Gulp, the beams ran not as he had expected but from chimney breast wall to opposite wall, so if he'd removed much more down would have come ceiling and all.
Lucky fellow, put the bricks back in sharpish though. :-)