——- The California mantis shrimp (Hemisquilla californiensis) lives in muddy burrows among the kelp forests of southern California. This species produces a low-frequency “rumble” through vibrations of muscles under the carapace. With my colleagues in the Patek Lab, I recorded many hours of these rumbles in the mantis shrimp’s natural environment, off the coast of Santa Catalina Island, California. We found that rumbles are produced in rhythmic sets, and that most rumbling takes place during crepuscular periods when individuals are most active. During certain recording periods, rumbles of differing frequency and temporal patterns were audible, suggesting that different individuals produce distinct sounds. We also observed that the frequently occurring boat noise in this habitat was louder than the mantis shrimp rumbles, an example of acoustic masking. This manuscript was published as a “featured article” in Aquatic Biology.