The Grennai are a telepathic species who are so far advanced telepathically that they have lost the ability to communicate verbally. Unlike most other telepathic species, Grennai telepathy sends images rather than words, allowing for a much higher rate of information exchange. Due to this fact, other telepathic species have difficulty communicating with the Cairn, though it is possible with training. Privacy was a concept unknown to the Cairn before they started to interact with the Federation. In some, there is a mutation in which some Grennai have no telepathy at all.