Once he had found his seat he removed his shoe and discovered a flattened black mass of chewing gum embedded deep in the zigzag tread of the sole. Upper lip arched in disgust, he was still picking, cutting, and scraping away with a pocket knife as the train began to move. Beneath the patina of grime, the gum was still slightly pink, like flesh, and the smell of peppermint was faint but distinct. How appalling, the intimate contact with the contents of a stranger’s mouth, the bottomless vulgarity of people who chewed gum and who let it fall from their lips where they stood.

Ian McEwan