And then, in a language humans were only beginning to understand, they continued their meeting.… People often said that cats were strange animals. Dogs waited at doors for their owners. Horses were trained to run, pull, or carry. Cows stood patiently in fields and produced milk. But a cat could spend an entire afternoon asleep on a windowsill, wake at sunset, stretch as though it had been summoned by some invisible authority, and walk out into the darkness without explaining where it was going. Mika lived with such a cat. His name was Sumi. Sumi wore no collar and had never shown the slightest interest in being walked. Every evening, he slipped through the garden gate and disappeared among the narrow streets of the neighborhood. Mika used to worry about him. Then, after reading more about modern feline behavior, he began to understand that Sumi’s independence was not quite the same thing as loneliness. Domestic cats are social...