Halliday & Matthiessen (1999: 155):
In the taxonomy of figures, the nature of the Medium is more criterial than that of any other participant or circumstance. For instance, if we consider processes such as ‘strew, spill, pour, sprinkle’, it is the Medium, not the Agent, which enables us to differentiate among them (cf. sprinkle + salt, spill/pour + water, coffee; strew + flowers); similarly with ‘bend, straighten, flatten; melt, freeze, evaporate, condense; crack, break, shatter’ and so on.