Okay, true story:

My brother is well known as being, well, outspoken, weird, and not given to suffering fools gladly. So when he was in college and a rabid vegetarian become overbearing in her statements about how animals felt pain and so plants were the only "ethical" things to eat, he took conducted an actual, scientifically grounded, experiment.

First, he hooked a couple of electrodes to his left arm, attached them to an oscilloscope (this was more than a few years ago, okay?), and stabbed himself in the arm with a sterilized scalpel. A friend recorded the 'scope readings of the pain.

After bandaging his arm (hey, I told you he was weird, but he didn't feel right about asking someone else to stab themself) he hooked the electrodes to a mature carrot and brutally YANKED it out of the ground.

Same sorts of 'scope readings as when he'd stabbed himself. He repeated the experiment on another carrot, but this time cut off the part sticking up above ground. He got the same "pain readings".

His conclusion was obvious: plants feel pain too.

(I also made some conclusions about my brother, but they were irrelevant to the basic experiment.)