It's one thing for CNN to explain what we're seeing in disturbing video come out of Iran. Getting firsthand accounts of what is happening on the ground, however, is incredibly dangerous. Ordinary Iranians are sending us photos, video and calling CNN at great personal risk. So we're protecting their identities as best we can. A student known to us only as "Mohammed" spoke by phone with CNN's Don Lemon about hundreds of people clashing with the feared militia known as the Basij, and why this moment in history is so important to his generation.

TV depends largely on visual images. But sometimes a video shot in darkness is more compelling - especially when you hear the terrifying audio. This video was sent to CNN by a trusted source inside Tehran. You can judge for yourself what it reveals.