However, the choice of who to re-direct the aggression to is rarely random. The choice of the recipient may indicate either 'I'm still higher ranking than you are' or 'if I get attacked someone in the attacker's network of allies will suffer for it'. I realize that these seem like anthropomorphic observations on my part, but these are not rare occurrences and a skilled observer can often predict who out of all the animals present at the scene will be the one attacked. If there is predictability and patterning there is more than a message of anger and frustration being sent. Another set of situations in which the function and the message can be quite different in primate communication occurs when the message only serves as a vehicle for the function.
Primates use communicative ploys to gain proximity to and interaction with desirable partners.
In one case from my own experience, two females were eyeing each other but a little nervous to approach closely. Then a young infant wandered in between them. One way of proceeding would have been for both females to groom the infant and thus gain proximity to each other and eventually end up grooming each other. In fact, in this case one female hit out at the infant, and it vocalized suddenly. Next the other female threatened the first who jumped back quickly, then began to grimace and teeth chatter, which are submissive and friendly affiliative gestures.