Train tracks and helium gas. 2 questions.

[Pixter]

q,1: the hero of a western movie listens for an oncoming train by putting his ear to the trck. why does this method give an early warning of the approach of a train?
a: My thaught are that any object that vibrates causes sound waves (due to compression waves in air..which are sound waves). so the train will make the tracks vibrate when it rolls on them, and because steel or whatever metal they use in train tracks leads the vibrations much faster then the air itself. one will be able to hear the vibrations on the tracks long before one can see the train...
[might have missed out on something special here, and if so could someone point it out or give me some pointers]

q.2: When you inhale helium, your voice becomes high and squeaky, why?
a: I know that helim lead sound waves 2,7 times faster than air. I think the answear has something to do with the sound bouncing in your troath.. so to say. can't really figure out why, but I don't think the frequencie changes because nothing would actually happen to the vocal chords themselves.
I can't really figure this out so some help would be nice. thanx

 

[Chi Meson]

q1, you are on the "right track." (har har har). Actually, you are totally correct.

q2, On the right track for this one too. Helium atoms are moving much faster than oxygen, CO2, and nitrogen molecules in the air. All I will say is that if you hear a higher pitch coming from your throat, then your vocal chords are vibrating faster.