Edgard Varèse, Density 21.5 (p.1, last line)

During the Twentieth Century, composers expanded the available sounds of the flute to include percussion-like effects. The most common of these is the key-click, pioneered by Edgard Varèse in his famous work for solo flute of 1938, Density 21.5. Key clicks can be performed by themselves; the flutist fingers a specific pitch and slaps a key without blowing (usually notated with an x notehead), or in combination with regular notes. Varèse has chosen the latter for this passage. Note the alternation of key-clicked notes (written with regular note heads with the + notation) with normally-articulated pitches.

Edward Taylor, Soliloquy (m. 78-9)

The tongue ram is a percussive device produced by completely covering the embouchure hole with the mouth and forcibly sealing it with the tongue, creating a pizzicato-like sound. Tongue rams are only effective in the first octave of the flute, and produce a pitch sounding a major seventh lower than the fingered note. The flute range can thus be extended to an octave below middle C. The composer will be advised not to write rapid successions of tongue rams, as the flutist will need about a third of a second to reset the tongue and air. Interspersing tongue rams in a very fast passage of regular notes is also not advisable, as they require just a bit of time to cover the embouchure hole completely. This passage from Edward Taylor’s Soliloquy features alternating use of key clicks (with x note heads) and tongue rams (diamond-shaped note heads, with resultant pitch in parentheses).

Andrián Pertout, Echoes from the Past (m. 58-9)

Another quasi-percussion effect possible on the flute is the tongue pizzicato. This effect is produced by fingering a specific pitch and producing a hard "T" with the tongue (the throat must be closed to avoid extra expulsion of air). This effect is more facile of execution than the tongue ram, as double-tonguing may be employed to produce quick streams of tongue pizzicati. Some flutists prefer to produce this sound with a forcible opening of the lips, in which case the term "lip pizzicato" is applicable. This passage from Andrián Pertout's Echoes from the Past illustrates an effective use of the tongue pizzicato. The notation pizz, combined with x note heads, leaves no doubt as to the composer’s intention.