Sulfur Hexafluoride

A scientist visited Jay Leno on the Tonight Show, and brought a dense gas (approximately 5 to 6 times heavier than air) called Sulfur Hexafluoride. The scientist called Sulfur Hexafluoride 'anti-helium'. Instead of making your voice really high, it makes your voice really low.

The gas is so dense, that when inhaled it fills the chamber of your mouth and because it transfer sound at such a low velocity it filters out all the high sounds in your voice!

Here's a few videos, the first one includes Jay Leno and Josh Duhamel using Sulfur Hexafluoride to make their voices lower, and the second includes a short clip of 'Mythbusters' Adam Savage using and explaining the effects of Helium and Sulfur Hexafluoride, and the last clip is of a scientist making an aluminum foil boat float on the dense gas.