Cheating and constraints of cheating are not limited to intraspecific interactions; it can also occur in a mutualistic relationship between two species. A common example is the mutualistic relationship between cleaner fish "Labroides dimidiatus" and reef fish. Bshary and Grutter found that cleaner wrasse prefers the client tissue mucus over ectoparasites. This creates a conflict between the cleaner fish and reef fish, because the reef fish only benefit when the cleaner fish eats the ectoparasites. Further studies revealed that in a lab setting, the cleaner fish undergoes behavioral change in face of deterrents against eating their preferential food. In several trials, the plate of their preferential food source was immediately removed when they eat it, to mimic "client fleeing" in natural settings. In other trials, the plate of their preferential food source chased the cleaner fish when they eat it, mimicking "client chasing" in natural setting. After only six learning trials, the cleaners learned to choose against their preference, indicating that punishment is potentially a very effective countermeasure against cheating in mutualistic relationships.