Season 1 Ep.43. When I was 6 or 7 years old, I already knew how to estimate the distance of a thunder storm. You count the time from the lightning to the thunder, it's 5 seconds per mile, or 3 seconds per kilometer. But when Lex, Bray, Amber and Dal look back to Hope Island, the flash and the bang are at the same time. Maybe it's something to do with time running backwards there?