Do you Imitate?
The curiosity of the gentleman who, seeing someone shrug their shoulders, instantaneously and voluntarily, shrugs his own shoulders, has elicited several similar accounts.
It may even occur when, for example, watching the news on TV and seeing a person shrug their shoulders – the viewer feels the urge to imitate.
Similar such behaviours include waving and blinking, with a further variation of “feeling grievous pain” on hearing someone describe falling over and injuring a limb.
This phenomenon has a name, Echopraxia, and could, it is thought, be related to copying behaviours common in infancy.