A skateboarder looks at a human-sized lab rat cage installed as part of the "Don't Be A Lab Rat" campaign to discourage youth marijuana use at the Denver Skate Park in Denver on August 12. The $2 million advertising campaign, aimed at warning 12 to 15-year olds about the risks marijuana use has on their developing brains, started on Monday, and is sponsored by the Colorado governor's office.  Reuters/Rick Wilking