I was cycling to work when I heard a loud clatter coming from somewhere around the drivechain on my bike. I pulled over and found a four cm long piece of metal stuck through my rear tyre. It looks like the spike had entered through the centre of the tyre and then been deflected by the tyre liner and come out through the side wall. I pulled the spike out and, since the tyre didn't start to deflate in any obvious way, I carried on to work. There's now a pretty big tear in the wide wall of the tyre though. It probably means another tyre that needs replacing because it was cut to pieces well before it even got close to wearing out.