I agree with bear, why are you sticking body parts in plants. BTW, the worm's response is reflex not pain. It does serve the same purpose as pain which is to protect, but is definitely not even close to the order of complexity of pain. The plant is also a reflexive reaction even more primitive than the worm. And no plants do not feel pain. I on the other hand speak from experience that touching a prickly pear cactus (plant) can really cause pain for me!
We are so conditioned by what we see in movies, TV and the well intended, but highly misguided environmental extremists to see all life on planet earth through the way we as humans view it. Bambi thinks, Nemo can talk (fish language of course, that Benji thinks like a human and that even as complex as they are, that chimpanzees experience the world like we do. I assure you that no other animal experiences life at the depth of complexity as do humans. This can be good and bad, but definitely vastly more complex.
Perhaps a more interesting discussion would be why runners would rather run in pain than not run at all and have no pain. That is a far more interesting subject.