The Gau beeja mantra originated from Gau tantra. The mantra is “Om Gaum”. It originated during the conversation between Lord Shiva and Goddess Parvati. This highly powerful mantra is chanted to protect earned Siddhis.
Vaak siddhi is when a person speaks something and that happens. Saraswati is said to be sitting on his tongue and his words carry so much power that what ever he says happens.
In ancient times persons possessing such a paranormal gift were known as Oracles. These Oracles where known to have a uncanny prophetic vision and were the favorites of the ruling class; who did not take any major decisions without their counsel; as their spoken words invariably turned out to be true.
Vaak Siddhi is the perfection of the sound projection. Guru Nanak explained it: ‘Through the mouth you utter a sound current, to which God listens with love.’