The Three Spines Stickleback Fish

It's a fish called the bony eared ass fish. Its brain weighs less than one, one thousandth of its body weight. Of all the animals that we've tried so far, this is the smallest compared to its size. But it has massive sort of ear canals. So the ear canals can grow bigger because the brain isn't there - which means you might call it its name and it might not understand it, but it will be able to hear it.