Echolocation frees dolphins and their ilk from the need for a two-dimensional alphabet. Though humans hear words as waveforms intended to be drawn and read as sequential glyphs, the sounds made by these creatures are vases sculpted upright in time, each experienced as a single, unique object. Meaning lies in the three-dimensional curvature of their forms, rather than in the ordering of symbols.
Despite their geometric nature, the words of this language do not exist in a one-to-one mapping with the forms they describe. The dolphin word for “coral reef” is experienced as a three-dimensional object, but it does not look and feel like a coral reef. Even so, objects can sometimes feel like certain words, and certain words can sometimes feel like other objects. The dolphin word for “shark” feels like it leads with a mouthful of teeth, yet so do the words for “jellyfish” and “kelp.”
Because they are marine mammals, dolphins never allow their entire body to sleep at once- some aspect of their consciousness must remain active at all times to keep them close to the surface. As such, their nervous system shuts down in shifts, allowing only half of the brain to dream at a time. This bifurcation lets them keep an eye out for predators, as falling asleep in open water can leave them vulnerable and exposed.
While the left half of the brain is asleep, the dolphin dreams of the universe of matter. Two parallel worlds appear before their senses simultaneously: one real, and one false. Though telling which is which is sometimes difficult, because there is clearly a schism, they always know when it is that they are dreaming.
During the right lobe’s slumber, however, the dolphin dreams instead of the universe of language. Here, there are no distinctly physical objects, nor concrete structures of any kind- yet the dream itself is still a three-dimensional space which can be experienced and explored.
Dolphins are aware of this duality in retrospect, but never during the course of dreaming itself. Both inner universes are equally vivid, and always more so than the real; as such, despite their difference in composition, it is impossible for sleeping dolphins to determine which half of their brain is currently awake.
Hibernating bears also contend with dream duality, though in different ways.
Human instruments hear only silence when dolphins speak of sea serpents.
River dolphins have a different word for mermaids than their saltwater cousins.