——- In this study, we investigated the effects of behavior, body size, and ambient noise on the anti-predator “rasp” signal produced by the California spiny lobster. We recorded sounds both in the tank and in the field, and lobsters were hand-held in all experiments. Although body size was not a major determinant of the acoustic qualities of the sound, behavior played a significant role. The lobster’s sound-producing apparatus is located at the base of each antenna; sounds are produced through stick-and-slip friction between each side’s plectrum and file. These animals can independently control the movement of each antenna and thus can produce rasps through one side only, or both sides concurrently. There were significant differences in the structure of the rasps recorded in tanks versus in the field. In the field, the high level of background noise means that rasps are audible at short distances only, an ideal quality for an antipredator signal. Overall, we found that both the behavior of the animals and the environment in which these sounds are used play important roles in the function of the sounds.