One of the most noticeable forms of mirroring is yawning - one person starts and it sets everyone off. Robert Provine found that yawning is so contagious you don't even need to see another person yawn - the sight of a wide-open mouth is enough to do it.
It was once thought that the purpose of yawning was to oxygenate the body but we now know that it's a form of mirroring that serves to create rapport with others and to avoid aggression - just as it also does for monkeys and chimps.
He found that, as with most other body organs, the heart appears to retain cellular memories, and this allows some patients to experience some of the emotions experienced by the heart donor.
Even more remarkably, he found some recipients also assume the same gestures and posture of the donor even though they have never seen the donor.
Non-verbally, mirroring says 'Look at me; I'm the same as you.