Display rules indicate such things as when to touch and where, when to smile and when to frown, and whether loud talking and expansive gestures or quietness and controlled movements should be used. All cultures have these and they typically vary even just slightly from one another. These are instilled in us from the beginning and let us know what behavior is acceptable and when. Cultural differences allow people to work together and bounce ideas off of one another, but they most also know how to appropriately interact with different cultures.
