The current theory posits that synesthetes’ brains have extra connections. When you see a word, your retina and optic nerve send that information to the visual cortex, which creates the image you see. Then your noggin’s face- and color-recognition unit, the fusiform gyrus, puts it into context. Extra connections there might simultaneously send signals to, say, both the color- and word-focused regions. Those extra pathways can pigment terms, weaponize musical notes, or even ruin a first date with a rather putrid-tasting name.