If you ever find yourself lost in the desert with your water running low, stay alert. We've encountered prickly Saguaros that seem to demand “Reach for the sky!” without any apparent reason. Were there heat-induced hallucinations or a drink or two involved? Perhaps. But the key takeaway is that it takes a cactus decades to grow to that height, so you can safely pass by. As for how we know this—well, that's another story.