Chaser, a border collie who lives in South Carolina, has the largest vocabulary of any known dog. She knows 1,022 nouns, a record that displays unexpected depths of the canine mind and may help explain how children acquire language. Children pick up about 10 new words a day until, by the time they leave high school, they know around 60,000 words. Chaser learned words more slowly but faced a harder task: Each sound was new and she had nothing to relate it to, whereas children learn words in a context that makes them easier to remember.