[shelanachium]

We all know we can sound like Donald Duck by breathing helium. Has anyone tried instead a very dense, harmless gas such as perfluorobutane - or even better perfluoroneopentane C(CF3)4 which is ten times denser than air? You should sound like a dinosaur (or as I imagine one to sound). I call these 'growl gases'. It should also be possible to sail a paper boat on one of these. Trivial I know...

[Borek]

I wonder if they are really so safe. I have no doubts they be harmless as in 'not toxic' but they will probably tend to occupy lower parts of lungs, making breathing inefficient.

http://www.chemicalforums.com/index.php?board=9;action=display;threadid=4698;start=msg20900#msg20900

[Mitch]

I remember someone doing this with a xenon compound, quite funny actually.

[jdurg]

I've done it before with sulfur hexafluoride which is an incredibly dense, yet chemically 'inert' gas.  It makes your voice get so low in pitch that it's almost impossible to hear it.  The gas was expelled by bending downwards over a chair and forcefully coughing it out.

[constant thinker]

I guess this is somewhat safe. Remember folks. If you can't breathe after inhaling these things. Invert your body and forcefully exhale.