Sulfur hexafluoride is basically the opposite of helium. It has a density of 6.12 g/L at sea level conditions, which is considerably higher than that of air. This means that when you inhale it, your voice gets creepily lower. However, inhalation of this gas is not recommended because it is difficult to get back out of your lungs once ingested. This, of course, hasn’t stopped people from doing it. Here are a couple of my favorite SF6 moments from the interwebs.