I'm not sure if there is a name for this, but I'm going to call them "cholla bombs." They are parts of the cholla cactus that have fallen, or broken off for some reason or another. While hiking near Plum Canyon in the afternoon, numerous times I would trip and find a chunk of cholla stuck to my pants or the sides of my shoes. At one point, I tripped and kicked up a piece of cholla straight into my left calf. After cursing in pain, I attempted to remove it from my throbbing leg. It was kind of like removing a band aid, but a little more painful. Once I realized that it was not going to come out by removing it slowly, I had to muster up the courage to pry it off my leg with a stick after a quick 3 count. A couple of days ago, I saw a video about visiting Anza Borrego and the park ranger suggested bringing a pair of tweezers and a fine toothed comb for sole purpose of removing parts of the cholla from pants. I'll have to remember that next time!