A number of times now we've seen scenes in which characters are present in each other's flashbacks (Jin and Sun in the airport with Jack; Sawyer at the police station at the same time as Boone, which I assume we're going to see the other side of in the second Sawyer episode).

Is there a hard-and-fast rule for when these are shot? Since everyone seems to be in the same shot, do you shoot scenes for both episodes at the time you shoot the earlier episode? the later episode? Or does it depend on the availability of locations and actors?

And how much of this overlap is planned before the "official" screenwriter of each episode drafts the script? It seems as if the writers have to collaborate very closely, even on the "off-island" flashbacks.

By the way, keep doing this as long as it stays this side of plausibility. It pulls all the threads together beautifully.