Synesthesia! A weird thing experienced only by unusual people, or by ordinary people on unusual drugs, or – is it something everybody has all the time? Are very low musical notes literally “dark”? Can food sound like something, like hot peppers going “ping” on your tongue? Why does it make sense to call a fork a “zrickrick” and a pillow a “baobwab”? Or does it? In 1688 William Molyneux asked John Locke whether a blind person who regained her vision would be able to distinguish a square from a circle by sight. Locke said no. Leibniz said yes. Who was right? This week Eric and Taylor puzzle over Molyneux’s question and a variety of other related and unrelated matters to do with musical temperament, linear perspective, and octopuses.