Yeah, and the problem is if you define “pain” too loosely, you’ll end up concluding plants feel pain. A Venus fly trap can close in response to an insect landing on it. That’s a response to a stimulus. Some plants release chemicals in response to damage or exhibit other responses that could be defined as pain.

You have to be really careful when using “the ability to feel pain” as a litmus test for the ethics of eating a particular organism. If you define it too tightly, you’ll conclude that it would be morally OK to eat a Neanderthal (something clearly conscious but also not human.) Too loosely, and you’ll conclude the only moral choice is starvation.