SDSU philosophy prof liked to tease us undergrads away from pious vegetarianism by telling the story of an experiment where researchers hooked a head of lettuce up to some electrodes and something like a heart monitor. When they approached the lettuce with a knife, the needle started to quiver, signaling the lettuce didn't want to to die.
Natalie Angier throws more water on any Pharisaical vegan fire with this NYT article noting our green friends can also call in reinforcements:
“I’m amazed at how fast some of these things happen,” said Consuelo M. De Moraes of Pennsylvania State University. Dr. De Moraes and her colleagues did labeling experiments to clock a plant’s systemic response time and found that, in less than 20 minutes from the moment the caterpillar had begun feeding on its leaves, the plant had plucked carbon from the air and forged defensive compounds from scratch.
Just because we humans can’t hear them doesn’t mean plants don’t howl. Some of the compounds that plants generate in response to insect mastication — their feedback, you might say — are volatile chemicals that serve as cries for help. Such airborne alarm calls have been shown to attract both large predatory insects like dragon flies, which delight in caterpillar meat, and tiny parasitic insects, which can infect a caterpillar and destroy it from within [Natalie Angier, "Sorry, Vegans: Brussel Sprouts Like to Live, Too," New York Times, 2009.12.21].
I've got bigger fish to fry than the food debate. Everything eats, and everything, including us, is eventually eaten—maybe by coyote or grizzly bear, more likely by lowly bacteria.
And now, if you'll excuse me, monkey bread and egg bake (heavy on the sausage!) await. Ah, the circle of life is so tasty!