(Training) Vocalizations
Vocalizations are any number of sounds believed to be produced by the bigfoot, such as howls, moans, growls, yells, whistles, and screams. Some sounds are believed to be warning signals, while others are thought to have various other meanings. It is thought by some that the bigfoot is able to mimic other animals, but given the lack of proof or even observation, this is pure speculation, as are many things bigfoot related.
Tree knocking, or wood knocking, is another sound attributed to bigfoot. The sound is believed to be made by a bigfoot striking a tree or log with a large stick, and does not originate from within the creature itself, like a vocalization.
The following screenshots are from a presentation done by the Mid-America Bigfoot Research Center based in part on an article by Alicia Bateman and used with her permission.