Halliday & Matthiessen (1999: 189):
The boundary between conscious and non-conscious, of course, is fluid and negotiable: different systems and different speakers (or the same speaker on different occasions), may draw it in different places. But the guiding principle is that ‘conscious’ means prototypically adult human and may be extended outwards (a) to babies, (b) to pets, and (c) to higher animals — as well as by rhetorical strategies of various kinds.