Halliday & Matthiessen (2004: 250) note that the Behaver ‘is typically a conscious being, like the Senser’, whereas ‘the Process is grammatically more like one of ‘doing’’.
So the grammar basically construes behaving, this blend of sensing and doing, this materialisation of mental processes, as Senser doing.
And what does this exteriorisation of sensing afford in terms of group activity?