[...] any organ, once existent and in so far as it is subject to voluntary control, can be utilized by man for secondary purposes.
- Sapir (1921), a pag.9

[...] all voluntary communication of ideas, aside from normal speech, is either a transfer [...] from the typical symbolism of language as spoken and heard or [...] involves the intermediary of truly linguistic symbolism.
- Sapir (1921), a pag.21

Observe the 'voluntary'. When we shout or grunt [...] we are no longer fixing vocal adjustments by voluntary control. Under these circumstances we are almost certain to hit on speech sounds that we could never learn to control in actual speech.
- Sapir (1921), a pag.45