[bumby]

"Experience" is the tough part to define here. Granted, it's not an easy answer but there are some smart thinkers who've tried. Here's an interesting take from the neuroscientist Vilayanur Ramachandran

"your withdrawal from a hot kettle is a different pain from the pain that you then contemplate. In the first case, the pain from withdrawal from a kettle, there is no qualia, no meta-representation."

From his framework, to truly "experience" pain, there needs to be a sense of self. You need higher levels of cognition for the "meta-representation" that causes suffering in our human conceptualization of the term. (There's some interesting brain lesion studies about people who lack this sense of self. They can witness their own body interacting with the environment but have no actual "experience" of the action; it's as if they are watching someone else perform it.) Everything more primitive to that higher cognitive function is just stimulus-response. For example, Gerald Engelman draws the line at lobsters in terms of what "experiences" pain and suffering. The implication being anything below that from a neural perspective would be cruelty-free to consume.