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You may have heard that you can get water from a cactus if you are ever lost and in a desert. Does it sound like a nice survival tip to store away, but is it really that easy? It turns out that a cactus is not actually a spine-covered basin of fresh water. Such a plant would not last long in an habitat filled with thirsty animals. Water is truly a precious resource in a desert, so, in addition to their spines, most cactus species further protect their spongy flesh with acids and potent alkaloids. These chemicals are usually too acrid for most humans to tolerate and are on the kidneys if ingested. The flesh of some cactus species can also cause vomiting, diarrhoea, or temporary paralysis — none of which is to your survival in an emergency situation. Cactus fruits are a better bet, though many are also unpalatable if eaten raw.