I was watching a television program and they mentioned micro-expressions. Since watching that program, I've come to realise that micro-expressions could very well be one of the significant distinguishing qualities of a great actor, especially a screen actor where everything is up close and personal. Micro-expressions are extremely small expressions, perhaps lasting one fifth of a second or even less. Consciously, we don't notice them. Unconsciously, we do and we're very much affected by them.
Most actors can reproduce expressions, some better than others, but even the best expressions may not trigger an emotional response in the viewing audience. I remember one of our teachers at Lee Strasberg commenting how tears from actors in general didn't do anything for him. Without the underlying pain, crying was simply an indicator without compelling emotion.
Actors who can reproduce the emotions of their character's situation will unconsciously reproduce the micro-expressions that come with those emotions. Those micro-expressions will then be unconsciously broadcast to the audience, making their acting captivating to watch and enabling the audience to empathise with and feel for the character.
Unfortunately, there's not a lot of emotional expression coming out of Hollywood's blockbusters today. Emotion seems to have taken a back seat to action (and the associated money-making franchises), and the English seem to be producing more emotionally sensitive movies and television programs than Hollywood. If Hollywood is not careful, a big chunk of the movie industry might just find a new home in England.
Anyway, today's point is that micro-expressions could very well be the mark of a great actor.