Katsuki Sekida from Zen Training - Methods and Philosophy

When all other ways of dissolving internal pressure are blocked, and the only way of discharging it is upon others, anger appears. When internal pressure finds no outlet and is driven inward, we feel sorrow and distress. Crying, barking (“You fool!”), and laughing are all modes of discharge of internal pressure through the drain called the respiratory organs. In laughing, as in expressing anger or sorrow, physical action plays a very important part.

If, when you are angry, someone by chance makes you laugh, you will forget your anger for a while; and when the old anger comes back you will find it much moderated. Part of the internal pressure has been physically discharged. When someone is crying, we feel touched with compassion, but from a physical point of view crying is the ego breaking wind and dissipating itself. However, when the ego does not consent to submit, and stubbornly maintains its position, then anger appears.