The "writing" of mind flayers, known as Qualith, isn't as simple as a set of symbols representing sounds or ideas. An inscription in Qualith captures the thoughts of its creator and psionically transmits the thoughts to a mind flayer who later reads the inscription by touching it with its tentacles. Mind flayers write in Qualith by psionically imprinting their messages on nonmagical, nonliving material they grasp or caress with their tentacles. The imprinting causes imperceptible surface changes to the object, and abrasion or degradation of the material can cause the inscription to fade and fail.
Qualith consists of four-line stanzas in interlocking blocks that form patterns other creatures cannot decipher. Touching an inscription can reveal fragments of the author's layered thoughts. A non-illithid can make an Intelligence check to understand part of it, but failure causes a severe headache and may cause madness.