I always thought cats licking each other was a social thing, and some cats just don't like other cats as much as some do. I always am glad to see my cats lick each other, because it means they like each other. And on the other hand, when one tries to get a small head lick fron another and the other shies away, I always feel bad for the poor cat that has just been shunned. And yes, it often leads to play with mine, too. Sometimes they lick until the other has a sopping wet spot.