<p>You can't boil blood by creating less pressure because the body is a contained environment. You could boil the saliva on someone's tongue but that's about it.
</p><p>As for all the other stuff, airbending has the potential to be a horrific element to control.
</p><p>You could cause someone's lung to collapse, or as we've seen with Zaheer, cause someone to stop breathing entirely. You could force all of the gasses dissolved in someone's blood to bubble out, which is known as "the bends" in scuba diving terms; in this same topic, you could control the gasses WITHIN someone's blood as an alternate form of Bloodbending.
</p><p>Sound is just vibrations traveling through a medium, it has nothing to do with air or anything really. Any bender could make a sound, say if an earthbender made sound through the ground it could also be transferred through the air and have the same effect if an airbender did it. Nothing special.
</p><p>Another thing is static electricity. Through friction and the separation of ionic charge in the atomosphere and the ground, lightning is formed. This means that through this same method, an airbender could bend lightning at a magnitude unheard of, vastly more powerful than that of a measly firebender can do.
</p><p>As for an airbending army? Hurricanes, storms, tornados, etc.....
</p><p>If airbenders were the antagonists in The Last Airbender, the war would have been over in a decade.
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