If you're a vegetarian or animal rights activist, chances are you've had this argument before. When you mention that you have compassion for animals, someone points out that plants have feelings too, and those carrots you were happily eating a second ago are actually screaming in some supersonic range. Sure, it's ridiculous. But could it be true?
In his book Primary Perception, fringe scientist Cleve Baxter described a number of experiments that he conducted with plants, testing their response to various stimuli. In many cases, the plants were attached to a polygraph (lie-detector), which measured the electrical impulses of their leaves. While the plants did respond with high levels of stress to certain events, they tended to react most strongly to wanton destruction such as an experimenter smashing or setting fire to an entire plant. Little response was recorded in relation to less dramatic acts like pulling off a few leaves. This research suggests that plants may feel something like pain, fear, or at least discomfort in certain cases. However, the amount of stress that plants undergo through normal farming practices may be insignificant, and in any case there might be ways that this impact could be reduced in the future.
Of course, these studies can hardly be considered conclusive. Luckily, it's not incredibly important to answer this question from an animal rights perspective, because regardless of the answer you're better off eating plants. The fact is, almost all animals used for food are herbivores, and the amount of plant matter they must eat in order to produce a significant amount of edible meat is many times higher than the amount of plants used in a vegetarian diet. So, whether those carrots are screaming or not, the plants and the animals should be thanking you for your compassionate choices.