When you play poker, (or other such games) and are rather good at it, it is because you can ‘read’ the ‘tells’ of the other players.
A lot of people have these expressions or gestures which give away their hand. Once you learn how to read ‘tells’ around the card table you can carry this into RL.
For example; when Trump is about to lie he makes a kind of lip twitch which seems a precursor to a smile. This is because he gets a lot of amusement by tricking people and great pleasure at having his lies believed.
Boris Johnson’s tell was the ‘um na um na’ kind of speech stagger. So he could say something like…”Um na um na I didn’t know um na that um na…” so you know that whatever he is about to deny, he is lying.
I’d love to play poker with these guys but am sure they don’t attempt any game in which they can give themselves away.