I agree JimD.. thats where the grunting and growling comes in, and, with a little luck, an impressive amount of weight, you many just intimidate some posers and half-assed gym goers too.
Its easy to forget about breathing tecnique, i learned a great deal about breathing during martial arts training that translated well to the gym. Another way to maintain focused breathing, especially during a heavy squat, is to take "cleansing breaths" before the movement, three or four deep, forceful breaths to oxygenate the blood. (sometimes you spit a little too, which is okay LOL)