Harmoniums are, according to The Sirens of Titan

The Sirens of Titan

The Sirens of Titan is a Hugo Award-nominated novel by Kurt Vonnegut, Jr., first published in 1959. His second novel, it involves issues of free will, omniscience, and the overall purpose of human history...

 by Kurt Vonnegut

Kurt Vonnegut

Kurt Vonnegut, Jr. was a 20th century American writer. His works such as Cat's Cradle , Slaughterhouse-Five and Breakfast of Champions blend satire, gallows humor and science fiction. He was known for his humanist beliefs and was honorary president of the American Humanist Association.-Early...

, the only form of life on the planet Mercury

Mercury (planet)

Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

. Harmoniums are paper-thin cave-dwellers that feed on nearly undectable vibrations in the planet, described as "Mercury's song" which are caused by the temperature difference between the planet's face exposed to the sun and the one facing outer space. Harmoniums are kite

Kite

A kite is a tethered aircraft. The necessary lift that makes the kite wing fly is generated when air flows over and under the kite's wing, producing low pressure above the wing and high pressure below it. This deflection also generates horizontal drag along the direction of the wind...

-sized and kite-shaped, and reproduce asexually

Asexual reproduction

Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...

 by flaking off in a manner not unlike dandruff

Dandruff

Dandruff is the shedding of dead skin cells from the scalp . Dandruff is sometimes caused by frequent exposure to extreme heat and cold. As it is normal for skin cells to die and flake off, a small amount of flaking is normal and common; about 487,000 cells/cm2 get released normally after...

. They have only the sense of touch, and also rudimentary telepathic powers

Telepathy

Telepathy , is the induction of mental states from one mind to another. The term was coined in 1882 by the classical scholar Fredric W. H. Myers, a founder of the Society for Psychical Research, and has remained more popular than the more-correct expression thought-transference...

capable of only two messages: "here I am, here I am, here I am," and "so glad you are, so glad you are, so glad you are."

Harmoniums are a semi-transparent blue, making the yellow walls of Mercury appear aquamarine beneath them. When they die, they shrivel up like dried fruit. They can die from feeding off too much vibration.

Boaz, a resident on Mercury, has an emotional connection with the species, collecting ones that stand out to him. He frequently holds concerts for the creatures, playing music, diluted through layers of material into the rock. If the harmoniums move too close to the concert they die "in ecstasy."