Apparently, only one study has tried to elucidate what is going on when a cat grooms (licks) another, which as you might know is called allogrooming. The study took place in 1998 (van den Bos).
The study concerned an indoor colony which consisted of 14 neutered male cats and 11 spayed females. The researchers made the interesting observation that the more aggressive individuals groomed the less aggressive individuals more often than the other way around. Also, in about one third of the allogrooming sessions the cat doing the grooming became aggressive towards the recipient of the grooming. This often occurred immediately after the grooming had taken place. This reminds me how domestic cats can sometimes lick their human companion followed by a bite. It might be the same thing as between cats.
Dr Bradshaw says that this behaviour is consistent with the idea that allogrooming in the domestic cat is a form of redirected aggression or dominance behaviour. The researchers also concluded that allogrooming is not a form of behaviour which is designed to maintain bonds between related cats.
I find this conclusion interesting and I want to disagree with it. Although, it interesting that the cat doing the grooming became aggressive sometimes. I wonder whether this was genuine aggression. I don’t know because we don’t know enough about the study but perhaps what might be happening is that the cat receiving the grooming may, at a certain stage towards the end become slightly agitated and that agitation is manifested in a certain form of behaviour directed at the grooming cat which kicks off a minor form of aggression in response.
Other studies I have read tell us that allogrooming is between “preferred” cats which indicates that cats that they are chosen to receive some grooming on the basis of friendship. That is the common sense reason but apparently it is not as simple as that.
Source: The Domestic Cat: The Biology of its Behaviour
Michael Broad wrote this post.