OTOH, I'm not sure whether it's the specific syllables, the specific intent, or the specific delivery that produces the effect. Would nonsense syllables produce the same effect if you believed that they would? Or is the human body biologically "tuned" to certain auditory stimuli?
FWIW, I've heard it said that "toh" in particular is used for what it sounds like--breaking through a barrier. "T" is the barrier holding the breath back--"o-o-o" is no resistance once you're past.