This great YouTube video puts a twist on an old party trick. We all know that inhaling helium gives you a high-pitched voice. It was funny when you were 5. It’s still funny. But do you know why helium has this effect?

Who better to answer that question than the Mythbusters? Adam Savage explains why helium changes your voice. He also shows how another gas can have a different, equally funny effect.

Don’t add this to your list of party tricks yet. The second gas he inhales is sulfur hexafluoride. Besides being expensive, it is dangerous if not handled properly.