A mirror-touch synesthete watching someone’s cheek being tapped feels a tap on their own cheek, either mirrored or on the matching side. The effect is automatic and can extend to watching pain, which makes some medical footage genuinely hard viewing.
The leading account ties it to overactive sensorimotor mirroring: the systems that simulate observed touch in everyone cross the threshold into actual sensation. Studies associate the trait with elevated empathy scores, though the direction of that relationship is still argued.
Prevalence estimates hover around 1 to 2 percent, making it more common than its low public profile suggests.