Cambridge Discovery Education Interactive Readers are the next generation of graded readers - captivating topics, high-impact video, and interactive exercises designed to motivate and engage. What do you really know about the sense of hearing? Learn all about the science of sound, the crazy noises animals make, and the loudest and quietest places on Earth. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1577. Lexile: 610L.