I would also like to point out that gorillas, at least, are demonstrably fully capable of cognizing suffering. Here's one doing it right here: http://www.youtube.com/watch?v=heTORvEyVKE&feature=PlayList&p=7D168F167A5398FB&index=0&playnext=1
Unless we think this is some kind of really, really complex reflex behavior. So why are we even having this argument?