You may have heard that turtles and tortoises, which lack an ear opening, are deaf, but that's not completely accurate. It's true that chelonians can't hear anywhere near as well as humans and many other species can. But they can detect certain types of sounds. Scientists who've used light microscopes to study the ear structure of marine turtles, for example, have found that their middle ears have a very thick eardrum-like membrane, which limits the frequency range they can perceive. But that adaptation is extremely efficient for bone conduction hearing at low frequencies, according to Behavior of Exotic Pets.

According to reptile expert Melissa Kaplan, Chelonians generally can perceive sounds in the 50 to 1,500 Hz range, compared to the typical human hearing range of 20 to 20,000 Hz. Our hard-shelled friends also can't differentiate loudness as well as we can. The spotted turtle (Clemmys guttata), for example, has a peak sensitivity of just 4 dB, compared to 120 dB in humans. The upshot is that while turtles and tortoises may not be able to appreciate, say, the nuances of Mahler's "Symphony No. 2," their sense of hearing is good enough to detect the presence of predators.