[extropy-chat] why so low?

[Spike]

Dog whistles and cat-B-gone screechers emit sounds
that are above the human hearing range.  I have some
deer alerts on my bike that also emit a sound higher
than can be heard by humans.  They supposedly work
on mooses, (meese?), elk and their ilk too.  
Can someone please explain why the human hearing 
range is so low?  Is it the lowest of all the beasts?  

Hey, grokiphany:  we know if we breathe helium, our 
voice pitch goes way up.  If we take a hoot of
xenon (density ~3x air) would not we get an octave
and a third lower?  If we talked like Lurch, would
the dog and the cat be able to hear us?

spike