In the jungles of South-East Asia entire bushes light up like Christmas trees, and in the Caribbean the seas glow with a luminous light. It's called bioluminescence - a term used to describe the many extraordinary creatures that turn themselves on in the dark. Watch fireflies in their hundreds' pulsing messages in the dark scuba dive in search of fish that-blink and flash, and swim among clouds of luminous plankton: And discover why the US Navy so very interested.