Am I the only person in the whole world who saw this and said "Well... DER!!!!!!!!!"
Lets look at the basic facts that even and average punter on streets can accept:
It's an animal
It has a brain
It has a nervous system (even if it is 'simple' it's still there)
YEAH IT FEELS PAIN!
I'm pretty certain that 'pain' is one of the basics for life... or at least having the ability to sustain it. I.E. "I'm not doing that dangerous thing (again), it hurts. Next time I might die / damage myself permanently and not be able to eat / reproduce / defend myself in the future" or "I'm scared to do that, it might hurt (see reasons above)" or "I'm getting away from this thing that hurts / might hurt in case (see reasons above)"
Was it really necessary to torture the poor buggers to find this out? "Oh look, if we burn it here it rubs it self. Maybe it feels pain?"
*Insert swear word of choice*