Question: How does Helium make your voice go weird?

Martin Zaltz Austwick answered on 15 Mar 2012:

The sound of your voice is affected by your body – the space the sound “echoes” in before it comes out of your mouth, if you like. The speed of sound through Helium is different from in air, and that changes the way it “echoes” in your body/mouth – it means higher pitches sound louder, and overall your speech sounds higher!