The coexistence between sharksuckers and sharks is poorly understood. Here, we studied the symbiotic client-cleaner relationship between Lemon Sharks, Negaprion brevirostris, and sharksuckers, Echeneis naucrates, with a focus on cleaning inside the sharks' mouths. Where observable, cleaning bouts were either initiated by a sharksucker moving along a shark's snout while maintaining body contact or by swimming in a “dance like” manner in front of the shark's eye without contact, until the shark gaped to allow entry. Sharksuckers interacting with sharks were typically in their first year of their life. While being cleaned by sharksuckers, Lemon Sharks were always seen in one of two positions: either lying flat on the sea floor, or propped on their pectoral fins. Cleaning bouts lasted significantly longer when the shark was propped. In bouts where the location of sharksucker activity within the mouth could be determined, cleaning activity exclusively occurred around the teeth of the upper jaws. In more than half of the bouts, the shark terminated the cleaning by spitting out the sharksucker. Overall, Lemon Sharks and sharksuckers show a highly evolved client-cleaner relationship with both able to influence and trigger the other's behavior.