Giant squid have the largest eyes on Earth, about the size of a basketball—but why do they need such big peepers? So they can see a sperm whale in time to escape its gaping jaws, researchers report online today in Current Biology. Seeing under water is tricky because light fades out at deeper depths and water makes distant objects disappear even before they are too small to see. But eyes are expensive to build and maintain, so such huge ones must serve a purpose. In the new study, researchers developed a computer model to look at what different-sized eyes could see at different water depths.