Despite having vocal cords, some animals make very little sound. These animals, called vocally quiet mammals, communicate with each other using clicks, whistles and other sounds that are inaudible to human ears.
In fact, all mammals except for dolphins and porpoises are vocally quiet. The exception is giraffes, who do have vocal cords but rarely use them. Instead, giraffes moan, hiss and produce a flutelike sound to communicate with each other.
Other animals that do not make any noise include clams, oysters and other shellfish, starfish and jellyfish. These creatures use other methods to communicate, such as vibrations in the water, chemical signals and body language.
Snails and slugs make no sounds, but they can communicate with other snails by transferring a mucus trail left on the outside of their bodies. Jellyfish, sea anemones and other marine invertebrates also do not make any sounds. They lack a brain and rely on other forms of communication, including magnetic fields and bioelectric currents that they generate within themselves.
Some snakes do not have vocal cords, but they can hiss and rattle their scales to communicate with other snakes. Hissing and rattling are often used as warning calls. Sloths also make a low-frequency shrill sound when they are frightened or in danger. However, a pine snake has been known to have local vocal chords and can make several sounds. The snakes that do not have any vocal cords typically rely on other methods of communication, such as body language and scent marking.
