Wow, after a slow paced episode last week, The Substitute really delivered.
The young boy was such an interesting figure as it could represent so many of the characters on the island: young Jacob, young Sawyer, an old Aaron and a young Locke. Personally I'm discounting the young Sawyer possibility but think any of the others could be valid.
The fact that he claimed: 'You knew the rules, you can't kill him' made me think this: the hydrogen bomb never exploded. Instead of this, the influx of electromagnetic energy that the 77ers were dangerously close to tapping into, escaped causing them to move in time to the present day.
What caused the reset and the alternate reality was Ben's killing of Jacob.
Please comment and let me know what you think.