in the belief that the genius was in the head and in the touching of the forehead in referring to him… we have probably the origin of the curious Roman custom of rubbing the forehead when blushing.
Onians argues that the Roman gesture of rubbing the forehead when blushing originates in the belief that the genius inhabits the head, making the act a propitiation of the indwelling daemon whom shame has disturbed.
, The origins of European thought about the body, the mind,, 1988thesis