We often experience that we know other people's condition, their feelings, their joy or sorrow, pleasure or displeasure, without their saying anything or making any sign. This is because, though it is not otherwise shown outwardly, it manifests in the breath. Sometimes if a very mirthful person comes among people who are all very sad, their mood changes. Sometimes if someone who is very gloomy comes into a gathering of people who are all very cheerful, without his saying anything, they all become sad. If someone laughs very much without any cause, other people want to laugh. If we see somebody yawn, even if we are not at all sleepy we want to yawn.