The vet searched for a thorn, bristle, scrap of metal, glass etc. What she found was an "abrasion", and a small one at that. Basically he had scraped his foot very lightly, and had irritated it by licking it too much. So, she washed it, put some antibiotics on it, covered it with gauze, tape and sent me home with a $60 bill.
When we got home, Treks milked it for all it was worth. He wouldn't bear weight on it, he walked around on 3 legs as if his other one was broken. It was worthy of an award. "And the Oscar goes to .....Treks for best performance as an injured dog in the drama category".