The Talosian singing plant was a plant native to Talos IV. It was a blue plant with a single, broad lily pad-shaped leaf on a long stem. It could be found growing among the many boulders and plains that made up the planet's surface.
As its structure vibrated in the near constant winds on the planet's surface, the Talosian singing plant emitted a beautiful, wailing chime, which was very pleasing to the ear. Holding the plant's leaf still in one's hands would cause the song to cease, but it would resume again once let go. Even Vulcans were not immune to finding pleasure in the sound.
The script of "The Cage" describes the noise produced by this kind of plant as "a musical flute-like sound" and characterizes the plant itself as "a plant with paper-thin rigid leaves which vibrate in the breeze. [Spock] blows on it, produces new musical notes." The script continues with a bracketed production note that reads, "These wind-plant sounds will identify and set mood for all our scenes on the surface of Talos IV."