[...Lido no blog Ciência ao Natural…O princípio é: uma máquina modificada capta o flash de outras ...]

This is good. Just plain honest video. fun stuff

I'm guessing he focuses on an object, then sets a flash on slave and has it fire through already developed film when someone else's flash fires. Makes sense, though you're depending on people using flash when they shouldn't be (to take a picture of an object that's too far away). Always fun to mess with people though.

I could have used one of these when my Dad was taking all those photos on family trips.