and technique from the middle ages to get their drugs across the border with a catapult. mexican officials seized that catapult and along with it 45 pounds of marijuana. it s being called the largest and longest psychological experiment in human history. tonight cnbc is breaking down the business and the science between the stacking and placing of tens of thousands of items on your grocery store shelves. tyler matheson joins us with a preview of cnbc s supermarkets inc. inside 5i hundra $500 bill machine. i m always looking in the wrong place for what i m trying to find. tell us how they make decisions, tyler? it s retailing 101. for example, why is the milk always at the back of the store? for one thing, it s heavy and they don t want to carry it it all the way to the front of the store, but for another, they know that most people come into