Pictures of nonverbal communication
As his emotional comfort increase still further, Jelani leans his torso as well as his head-neck unit towards the man. The man of course is doing the same thing - they are mirroring each other. Again, who initiated this? - It would be valuable to know. With respect to human behavior, this touching of the heads and shoulders (of course this is not quite occurring here because of the thick glass) during similar moments will amplify any rapport already established (thus it's one example of what is known as a "Rapport Amplifier").
It's of profound importance that at least some modestly significant level of rapport must have existed prior to this moment - otherwise if one person attempts such nonverbal behavior it will be interpreted as a form of aggression or at the very least "false intimacy" (asymmetrical intimacy) by most everyone (and certainly animals).
Head-neck tilting (particularly toward each other during a shared experience) indicates a level of friendly, emotional-vulnerability (e.g., "I'm don't feel threatened by you.", "I trust you", "I feel comfortable with you", "I'm letting you into my world."). And while the thick glass certainly facilitates feelings of safety and protection for both primates, such head-neck tilting towards another never occurs when a person/animal feels threatened.
If you watch Jelani's left hand/arm, he appears to gesture several times. Some people have interpreted this movement (including a woman heard describing this to another onlooker) as a signal for the man to advance to the next photo. This may indeed be true, however we would need to see a longer duration sample (with a better view) as well as other examples of Jelani's behavior to be sure.
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Why was physical appearance important in Roman culture? What does the portrait bust of Matidia communicate? | Yahoo Answers
I'd say that bust communicates her rank (she was related to Trajan) and perhaps also motherly qualities. I may simply be reading this into it as those were traits that would have been valued in women in Roman society, but that's what I see.