Rice is responsible for feeding half the world, or more than 3.5 billion people. In other words, rice is important. A tweak to how the grain is grown, sold or eaten can send ripples through the world economy. Take Thailand, which supplies 30 percent of the world's rice. Government subsidies there threaten to raise the price of putting dinner on the table in Mexico. GlobalPost takes a closer look at a tiny grain with a giant footprint.