At particular sites, an itchy individual can attract the attention of the bluestreak cleaner wrasse—a slender fish, with blue and yellow markings and a prominent black stripe. On seeing these colors, the itchy “client” strikes a specific pose, allowing the wrasse to snake across its body, mouth, and gills, picking off parasites and dead skin along the way. The wrasse gets a meal. The client gets exfoliated. A single wrasse works for around four hours a day, and in that time, it can inspect more than 2,000 clients.