Few people can arrange such meetings between a celebrities and 'commoners' as can Ellen DeGeneres. And for many people, the video included above is very emotionally evoking (and thus a barometer of the viewers' empathy).
While recovering from wounds he received during the Orlando nightclub (Pulse) shooting, Tony Marrero found Katy Perry's music to be a source of strength and inspiration. In addition to all the other emotions and the corresponding body language signs which are natural in such a surprise scenario, this interaction on Ellen's show also showcases a rarely discussed yet common nonverbal behavior.
Ellen (beginning at 0:18): "It is, it is a beautiful song - and ah, have you met Katy yet or no?"
Mr. Marrero: "No."
Ellen: "You wanna meet Katie? [pause] Katy!"
During 0:23 - 0:25, just after Ellen says, "You wanna meet Katie?", Tony Marrero alternates the gaze of his eyes - while looking fairly straight ahead, but with additional quick, superimposed, lateral movements (Saccades) - jerking back and forth several times. When his eyes shift left he appears to be focused on Ellen - but when he shifts right, he's focused at a middle distance (which is more common).
This relatively subtle and short-lived, rapid flickering motion of the eyes back and forth is an epiphenomenon of emotional processing. This is signaling that although the 'logical brain' may realize what's occurring, the 'emotional brain' has yet to fully grasp what's transpiring.
Although in this example we see the rest of Mr. Marrero's face is for this brief moment, relatively emotionally neutral - it's also quite common to have a 'Dropped Jaw' (aka 'Slack Jaw') configuration of the mouth (with no teeth showing) as well as eyelids opened wider than baseline. When sincere (as is seen in this example), these "Emotional Processing Saccades" rapidly give way to other powerful facial expressions.
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