Graffiti on walls around Havana telling Cubans "you need to be happy" has encouraged introspection and inspiration in a country where censorship has forced many street artists to emigrate or abandon their work.
The simple but striking message that began appearing more than a year ago is the creation of "Mr. Sad," a 27-year-old sociologist who, under the cover of anonymity, pushes the limits of rebellion on the communist-run island.
