There is no significant difference between 'pain' as perceived by animals, plants, humans or malware.
Actually, there is. In psychology and neuroscience there are accepted ways to measure pain behaviourally. Crudely speaking, humans and other complex animals pass more of these tests than plants or computer programs (mostly). These fields make a distinction between simple nociception, and awareness of pain. An animal with nociception will reflexively withdraw from damaging stimuli, but an animal with an awareness of pain can respond in more complex ways.
For example, imagine that there is a rat in a cage with two troughs of water. One is plain water and the other is water with a pain-killer dissolved in it. A healthy rat will tend to drink from the normal trough, but a rat with inflamed joints will tend to drink from the trough with pain-killer in it. This ability to make trade-offs is clearly something more than a simple reflexive response to harmful stimuli. Note also that pain-killing drugs are not something the rat has evolved to deal with. Plants do not show this kind of flexibility in their behaviour, but many complex animals (including fish and crustaceans) do.
N0body said:
Really, we should solve the issues within our own societies and cultures (yeah, I know, also not likely to happen in any of our lifetimes unless something miraculous happens) before we start trying to hammer away at the rights of other lifeforms (possibly including AI, when it eventually meets enough criteria to be 'intelligent').
Maybe not. If things like cows, chickens, and pigs can suffer anywhere near as much as humans can, then animal farming is probably where humans are causing the most suffering, simply because there are many billions of animals involved.