You can torture someone by growing bamboo into them (something that apparently happened in WWII). I love me my Mythbusters on the Discovery channel. They proved that within only 3 days, pointy, piercing shoots can grow many inches into a human torso. After a few weeks, a 12 foot stalk will be high above you.
I've always wanted to find a way to meld my horticultural interests with my slightly therapeutic / illegal fantasies.