SO ENDS this first of two weekends on synesthesia. When you buy a car, in general, the more complicated it is, the more there is that can malfunction. As engines go, the human body is about as complicated as they come, with millions of control points that can malfunction. In this regard, it is surprising that it works at all. It is likely that many functional faults do not let the zygote get beyond the starting blocks, and they simply vanish.