Dear Matthew Alice: How exactly does the gas helium make the pitch of your voice change? — Dave R., San Diego
That intriguing cartoon character effect isn’t caused by any strange workings of helium on your vocal cords. When you set them vibrating, the frequency is the same as usual. It’s just that as the sound waves are launched through your throat and mouth filled with the lighter helium, they travel faster. That raises the pitch that makes you sound like Minnie Mouse.