“Sonar users can sense the bottom and sides of the ocean—islands, seamounts, and coasts—as well as each other, getting detailed pictures of the shapes and inner structures (as in ultrasound scans of human pregnancies—ultrasound is sonar) of potential prey, social partners, and competitors. Sonar can also alert them to the presence of predators, but primarily the sonar of the toothed whales is about finding food.”