Carson’s strangely immobile face and body in the wings may or may not have been due to an ingested sedative, but his immobility, unresponsiveness and seeming confusion as he hesitated backstage matched the symptoms of sedation,” says Givens. In past months Carson has told violent stories from his past that he couldn’t support, floated wild theories about everything from Pyramids to pyramid schemes, and left voters of both parties generally confused.

Ben Carson's strange debate entrance – stage fright or sedation?

At the level of US presidential politics, a single gesture can be worth a thousand words. George HW Bush’s impatient downward glance at his wristwatch in the 1992 presidential debate, and Dan Quayle’s Adam’s apple jump in the 1988 vice-presidential debate – as Lloyd Bentsen said “You’re no Jack Kennedy” – come to mind. At last night’s debate at Saint Anselm College in New Hampshire, another type of behavior stood out as a potent nonverbal signal. The specific sign was immobility.

The debate began as one by one the seven candidates were called to the podium. The first one called, New Jersey governor Chris Christie, bullishly strode past the curtain with no hesitation at all. The second to be called, retired neurosurgeon Ben Carson, not only hesitated, but became starkly immobile – indeed catatonic – and waited in the curtained wings offstage. After viewing the video several times, my analysis of Carson’s strange behavior – conjectural and based on body language alone – points in two directions: either severe stage fright or momentary confusion, possibly brought on by sedation.

Stage fright involves a sudden involuntary cessation of body movement, usually in response to a stimulus of fear related to public speaking. As he hesitated in the wings after hearing his name called, Carson’s entire body froze. He stood flat-footed with his torso locked in the upright position, hands tightly clasped and arms pulled in flat against his lower abdomen. The freeze reaction is a protective reflex controlled by the brain’s amygdala. In it, the body may automatically tense up as the nervous system mobilizes either to fight or flee. Carson telegraphed an impulse toward the latter option but was apparently unable to move.

Sedation involves a drug-induced blockage of anxiety and fear. In mild doses, it aids relaxation and mitigates the effects of stranger anxiety and stage fright. Carson’s strangely immobile face and body in the wings may or may not have been due to an ingested sedative, but his immobility, unresponsiveness and seeming confusion as he hesitated backstage matched the symptoms of sedation.