Synesthesia is a condition where the brain's sensory pathways are crossed. In other words, synesthetes can smell a color, taste a sound, and so on.
The book itself is a connotative representation of a collection of journal articles, medical studies, and personal accounts of actual synesthetes.
The book explores ways to give the reader a taste of what it feels like to have their senses manipulated. This includes using textured paper, alternating shapes for text blocks, replacing folios with sensual words ("sandpaper," "screech," "paprika"), creating textures through different type weights, and even spraying the front and back covers with a heavy perfume.