Halliday & Matthiessen (1999: 142):
There are some behavioural processes that are agnate to cognitive ones (pondering, puzzling, meditating) but none that are agnate to desiderative or emotive ones. (Behavioural processes of giggling, laughing, crying, smiling and the like are outward manifestations of emotions; but they are not active variants of inert emotive processing such as rejoicing, grieving, and fearing.