The memory that haunts me most about 9/11 is not from that day, but from watching the incredible documentary by Jules & Gedeon Naudet entitled 9/11. These two French brothers started making a film about a rookie NYC fireman and ended up filming the the events of that day at Ground Zero. One scene depicts firefighters sifting through rubble, while in the background you can hear this eerie, continuous sound. The narrator identifies the faint beeping as the electronic emitters that firefighters wear to help locate them in a collapsed building. The sound went from faint to deafening in a split second. God bless those who gave their lives trying to save the lives of others.
