Question: Why/ How does Helium makes voices higher?

Christina Pagel answered on 26 Jun 2013:

The key thing about helium is that it is lighter (less dense) than air – and the sound waves move faster through helium than they do through air… so when you speak after inhaling helium, the sound waves from your vocal cords travel through helium and so more quickly, than they normally do. This makes your voice sound squeaky to other people…