Ever seen a Jumping Cactus?
You'll never get the little spines completely out. They just keep going deeper into your skin until they finally dissolve months later. And talk about painful...YES THEY ARE!
The shallow root system spreads out just below the desert surface and if you close enough to step on a root, WHAMO! The cactus will spring toward you in some cases. Back during the Apache wars with our government, the women would gather blankets full of these cholla balls and dump them on the US Calvary from the cliffs high above. The horses would go wild throwing off soldiers and running off away from the riders.
Bunk you say?
Try brushing a patent leather shoe against one of these cacti and watch what happens. Just one thing. Don't get too close while doing it!