Depends on how narrow your definition of "pain" is. Take a plant and put a sharp needle into its growth path. Many plats will avoid it and adjust their growth

Depends on how narrow your definition of "pain" is. Take a plant and put a sharp needle into its growth path. Many plats will avoid it and adjust their growth path, once they got into contact. Just like a human, a dog or a fish. The time scale is different, the effect is the same. It's a sensation that leads to avoidance of a certain negative stimulus.