Just what was that mysterious substance Marco Rubio popped into his mouth during the latest Republican debate on CNN?

While attention was focused on another debater, a video shows Rubio subtly slipping something out of his right pocket and popping it in his mouth.

Pundits have made all sorts of suggestions:

"It was a Hillary Clinton anti-choking throat lozenge."

"The pills keep his body from rejecting the control chip in his brain."

"Don't be ridiculous guys, robots can't take pills."

"Who would want a president that needs pills to keep him in control of his own head?"

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Armchair analysts have suggested every possible pharmaceutical option imaginable (legal or illegal, addictive or otherwise), but, of course, no one will ever know except Rubio himself.

This is not the first time Rubio's awkwardness on camera has been noted. He often takes heat for his verbal "short circuits" in which he repeats the same phrase over and over, earning him the moniker 'Marco Roboto.'

Over a series of back-to-back interviews last Friday with ABC, CBS and NBC, Rubio called Donald Trump a "con artist" more than a dozen times.

Three years ago he famously reached for a water bottle and took a quick swig in the middle of the Republican response to Obama's State of the Union speech.