Tongue pizzicato is a technique that results in two very short notes at the same time. It is performed by using only the air in the oral cavity to “snap” the tongue, creating a rapid “tk”-sound with the tongue placed in the upper part of the oral cavity. Normal embouchure is used.
The highest pitch is dominates the sound, and with the two parts of the sound one can manipulate the pitch, also independent of each other to some degree.
I have chosen to notate this playing technique with the keynote is notated either as a conventional note, or a note without stems, but then with a line that indicates the duration of the note. The notated keynote also defines the fingering of the note. The high pitch is notated as flageolets since they are based on the overtones of the keynote (or fundamental tone).
This playing technique has some dynamic limitations, and is difficult to play especially loud. Since the keynote is relatively difficult to hear, it will easily escape the listeners’ attention.