Greeted with a flat tyre this am
This is evidently why
That is a 'biggy'!!! 
As you can see, tyre had loads of life left too
I think it is a nail ... might be a bit of random copper ...
I just pumped it up again for now and rode on it anyway ... jobs a gooden!!
Tempted just to leave it in there and just pump the tyre up every now and then!!