Filming in progress - nail in my shoe

On the second day of our filming we were on the set filming (Tooting Bec Station). Shooting started at 7:40am and continued till 8:40am.
As we were filming I felt something in my shoe. I took my shoe off and cleared the inside. I assumed it was a stone of some sort. Then I put my shoe back on and I could still feel something digging in to my foot. I took the shoe off again and discovered there was a nail inside my shoe !