Sulfur hexafluoride
It is used in electronics and various electrical devices. It can be used in the body since it is not toxic. It can be used as a test gas to look where gas flows in a heater system, for example. It is detected easily. It is used in some torpedoes. Lithium is one of the only things that reacts with sulfur hexafluoride. Sulfur hexafluoride is sprayed on lithium. This makes the lithium very hot. It creates steam from water and shoots the torpedo. It can be breathed in to make the voice deeper. This is the opposite of breathing in helium gas.