Thanks for your comment. The Flash is pretty complicated. Creatures within range of the lightning only appear when the button is pressed, not during cooldown. Walking while the flash is activated is not a good idea. It's easy to go too far forward. The hallway is 10m long and the flash only has a range of 3m. I do it very carefully. I flash, I mark in my head where the range of the flash ends on the wall, walk towards that point and wait until I can flash again. Using this method I can ensure that I only run 3m.