I was visiting Shanghai recently. One afternoon, while sitting on the sofa, I inadvertently brushed a family member's arm. To my surprise, I felt an unnatural tingling from his skin—quite like a mild version of the shock from a (toy) shock pen or the slightly numbing vibration from an electric shaver. I could consistently feel the tingling by running my knuckle lightly across the family member's skin.
The family member had been using an iPod Touch plugged into a Chinese power strip via the stock Apple charger. The tingling persisted as long as at least one part of his body contacted the iPod and even when he touched the metal end of the charging cable directly with his fingertips.
- The tingling persisted when he stood on a plastic stool instead of the sofa.
- The tingling did not appear when we plugged the iPod into a power outlet at a hotel we later visited in a different city in China.
Unfortunately, I am no longer in China, so I will not be able to conduct additional tests. Does anyone have a scientific explanation for this phenomenon as well as what might cause it to occur only occasionally?