Forgive me if I have misrepresented Singer. So it seems that what distinguishes humans from other sentient beings is self-awareness. OK, I need ti read a few more things written by Singer. I've just read some articles, in on of which he states that a new-born babby is actually of less value (until they acquire consciousness) than a sentient and conscious animal. But is the distinguishing trait "consciousness", as I understood from the article, or "self-consciousness", which is the faculty that allows the human to value his or her life and therefore be aware of what they are losing? I'm just trying to get my head around this one.

If it is "self" awareness, then that is a big difference indeed. Have any animals (the higher primates for example) bee shown to be self aware? How do they react when they look at themselves in a mirror? Dogs and cats show no sign of such awareness.