O'neill Boardshort..

I bought swimming short this afternoon.. Only I discovered there was some kind of plastic 'saw' attached to the right sidepocket... There was some sort of nail in it which you could slide open.
I wonder where this is used for? I guess it has something to do with surfing, but as I am not actually doing that, I thought I could post it here.
I wonder where this is used for? I guess it has something to do with surfing, but as I am not actually doing that, I thought I could post it here.