"Shape your lips like a crow’s beak" and then stick your tongue out and roll iy into a U-shape, in which the sides of the tongue are curled upwards so that it resembles a tube open in its end.

This mudra is particularly associated with Shitali (refreshing breathing) or Vatasara Dhauti.

More generally, it is associated with all practices requiring a concentration on the heart center.

Pers. Notes:

The tongue consists of sixteen muscles.

The hypoglossal nucleus contains motor neurones innervating the muscles of the tongue via the hypoglossal nerve.

The caudal raphe also play a role in controlling the tongue.