The reality is: we can make an educated guess. Even though consciousness is not understood, it seems to require complex brain functions. I think the important

The reality is: we can make an educated guess. Even though consciousness is not understood, it seems to require complex brain functions. I think the important part here is making a clear distinction between reactions to noxious stimuli and the actual conscious experience of pain. That is where the discussion is. The fact that something reacts to noxious stimuli (like amooebas sometimes do) is not a reason enough for moral consideration.