In the dismal warehouse for hopeless cases known as Ward 23, he met a pair of identical twins named George and Charles Finn who had been variously diagnosed as autistic, schizophrenic, and mentally retarded. Despite the impoverishment of their surroundings, the twins carried a glory of numerical symmetry in their heads. "Give us a date!" they would cry in unison, and they were instantly able to calculate the day of the week for any date in a multiple-thousand-year span. As they executed these seemingly impossible cogitations, they would focus their attention inward — their eyes darting back and forth behind thick glasses — as if they were consulting an internal calendar that spanned dozens of millennia or more. The twins' calendar-calculating abilities were just one aspect of their extraordinary cognitive gifts. The next time that Sacks saw the twins, they were raptly enjoying a conversation that consisted solely of numbers. George would utter a string of digits, and Charles would turn them over in his mind and nod; then Charles would reply in similar fashion, and George would smile approvingly. In a case history published twenty years later in The Man Who Mistook His Wife for a Hat, Sacks wrote that the brothers (called John and Michael in the book) looked like "two connoisseurs wine-tasting, sharing rare tastes, rare appreciations." At first, he had no idea what they were doing, but he took notes on these cryptic exchanges anyway.