"Either you buy into it or you don't, " said Mr. Ruhf, who came up with the idea for Molecule after sampling a similar store in California.

WSJ: Something in the Water? Tapping an Idea in New York City

Just inside the entrance to the Bodega Aurrera store in Mexico City's lower-class Naucalpan neighborhood sit two shopping carts filled with the same sampling of products--things like Kellogg's Corn Flakes and a dozen eggs.

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