A prickly pear cactus consists of a number of flat, tear-shaped, green pads, each complete with a bunch of stickers growing out from it. If you hack away at a prickly pear cactus and leave one or more of the pads lying on the ground, it will eventually form its own roots, and start growing again. Prickly pear cacti are often found growing in patches throughout the desert, and in my experience are usually no more than a few feet high (although they will grow rather large given enough time). If there's nothing better around, and they're very thirsty, cows will sometimes take a bite out of a prickly pear.