Metacommunication is a communication qualifier: a way of contextually qualifying behaviors that follow.
Cleaner fish sport a uniform that identifies them by occupation. They have a contrast-enhancing black lateral body stripe that non-cleaning fish lack. Clients also recognize cleaners by their colors, particularly blue and yellow on certain body parts. These characteristic colors make the highest contrast against a reef background.
Cleaner fish dance before a potential client to signal their intent; a metacommunication that induces the much larger fish to reserve its predatory instinct and wait passively to be cleaned.
Having recognized the uniform and advertisement, a potential client fish that might otherwise consider a cleaner a decent meal instead decides to communicate an all-clear signal for cleaning: another metacommunication of intent. After all, food isn’t hard to find on the reef; but a good cleaning – well, that’s a service.
When a fish has had enough of having its mouth cleaned, it jerks its jaw in a certain way to tell the cleaner that it is time to move on. The otherwise risky marine ectoparasite removal business relies upon interspecies metacommunication.