Why does helium make your voice go higher?

Question: Why does helium make your voice go higher?
- Keywords:
  helium,
  higher,
  voice
Asked by zanibani to Murray, Sarah on 25 Mar 2011.
- Sarah Thomas answered on 25 Mar 2011:
  
  Breathing in helium does not affect the pitch of your voice, but it can make your voice sound squeaky! This is because the helium changes the resonance (or vibrations) of your vocal cords! But it wears off quickly!!

Question: Why does helium make your voice go higher?