It seems clear these are zoo monkeys. Even though there is no literal cage, compositionally, they are trapped in a box going round and round, as if pacing, as zoo animals (particularly the more intelligent mammals) tend to do. It is monotonous, but not a torturous monotony, at least for the monkey closer to us. He looks directly at us and smiles as if to say "Hey there."
The monkey in the back is a different story. Her face expresses not only quiet reflection, but deep melancholy. I find myself wondering if this is her typical state of mind, or if something specific occupies her thoughts. I almost feel guilty staring at her, as I sometimes do when I've joined a crowd of people gawking at a mother orangutan nursing her newborn infant, or a grumpy old gorilla with his back turned deliberately to the crowd.
What strangeness, to live a life on display. What a joy for the exhibitionist. What a nightmare for the introvert.