This is a combined mantra (incantation) and asana (ritual posture) for invoking or resonating with the energies of Bes  Kali (and/or other such primordial deities -eg. Pan, Shiva, Atum); it stretches and strengthens the tongue for Kechari, a tantric yogic exercise for energy circulation which is included in this posture.

 Bes is the Ancient Egyptian dwarf-God of music, dance and childbirth, who is often used to represent the pre-civilization Shamanic or Primordial Aeon. Kali is the Hindu primal Mother Goddess from which all things sprang. Both are usually depicted in ancient artworks with their tongues out.

 Stand with left foot facing outwards to the left and right foot facing out right, bend the knees into right angles; echo this with the arms, also facing outwards to each side in L shapes.

This is the traditional Thelemic/Maatian posture for Bes and is used in Nema's 6-fold banishment (into-which the following can be incorporated). Now add the mantra and accompanying mouth mudra:

 After a few preparatory deep breaths, Pull the tongue as far back in the throat as possible while inhaling deeply. Accompany this with an 'Aaaaahhh' sound, more breathed than spoken. Pause.

 When this can be taken no further, expel the breath with a forceful 'Haaa!' sound while sticking out the tongue. Towards the end of this exhalation the tongue is to be pushed out as far as possible, stretching the muscles to their full extent (if it hurts a bit you're doing it properly!).
 Repeat this process three times.

 The fragnum lignum web at the bottom of the tongue will rub against the bottom front teeth. If this exercise is done regularly (I suggest at least once daily) this ligament will gradually wear away, allowing greater flexibility of the tongue. Thus Kechari, the traditional Yogic technique of deep breathing with the tongue at the back of the throat, can be performed more effectively, as the tongue can fold far enough back into the throat to stimulate the pituitary gland there.  This is a 'self-mating' exercise which produces Amrita nectar in the throat and creates the 'Microcosmic Orbit' (Taoist term) to circulate Prana/energy throughout the body.

Illustration by Frater Sandan

The tongue mudra-mantra can be also be performed without the full body asana.

 The mantra 'AHA' is the Word of the primal aeon or Dreamtime, and the double-wanded (hermaphroditic) form of the Pan-ic mantra 'Ha!' and thus puts one in touch with primal sexual/creative essence.
Ah and Ha are also the sounds of the first and last letters of the Sanskrit alphabet, so the breath as the beginning and the end, the Alpha and Omega.
Additionally, as revealed in a commentary on the 29th Book of the Tantraloka:    Ah is the sound of Shiva and Ha that of Shakti, so the ultimate union of energy and consciousness is expressed. This is the rise of the Kundalini Shakti to the Crown (Shiva) within the individual (represented by Ardhanasrishvara the Hindu hermaphrodite God/dess), which can indeed be facilitated by advanced Khechari.
This AHA mantrasana is explored in greater depth in Orryelle's book, 'A Brief HirStory of TimemiT fo yrotSriH feirB A' <yrotsreh.htm> , including its uses within ritual contexts.

Orryelle Defenestrate-Bascule is instigator of The HermAphroditic ChAOrder of the Silver Dusk  , a movement focused on artistic/intuitive magick to counterpoint the scientific/rational system of the Hermetic Order of the Golden Dawn.

Orryelle Defenestrate is 2'3' Supreme Fool/Magus of The Order of ChAos. More of his Rite-ings, along with artwork and ritual theatre, can be found on his site The Mutation Parlour; and his esoteric poetry in the Research section of the new SSS site.