I picked up a thorn this
I picked up a thorn this summer while out on the meadow barefoot. I felt the prick when I stepped on it but it wasn't soooo painful, so I kept running. After about another Km, it really did start hurting, so I hobbled home and began trying to remove it. Couldn't see it in there anywhere. After the weekend, I went to the doc to get it removed, but she couldn't see anything in there either. She told me that if there really is something embedded, and she wasn't convinced, then it's so deep that I'd have to go to a surgeon to get it removed. I didn't want to do that, so I just waited.
And waited.
There was no swelling, no real visible clue that anything was wrong but after two weeks, it still hurt like hell to step on that spot (between 2nd and 3rd toe, deep down in the ball of my foot). I convinced myself that it was some kind of bruise...
After three weeks, though, I was poking around the wound area and saw a little white thing. I picked at it a bit and asked my wife to get some tweezers. She pulled on it and a bleached out, softened, 1cm thorn came out. I suspect it was from a raspberry vine, the only thorny thing on the fields here. As soon as it came out - relief! All was 100% better and I could run barefoot again the next day.
Moral of the story: If you DO step on something like that, stop and remove it immediately. That's all I had to do. But, by running on it, I forced it right down deep into my foot. I think it was down there between the first joints of the toes, maybe stuck in some muscle or something...