Caltrop or calthrop. Large numbers of them would be scattered on a road or trail to slow down pursuit by cavalry. When a horse stepped on one, it would bruise or puncture the sole of the hoof and make the horse go instantly lame.
Three men and one woman picking huckleberries using bark baskets. They are, left to right: Rev. Jesse Laws, Mona Roberts, Harmon Roberts, and Tom Faulkner.