"Lost" has been known for going down every possible rabbit hole, but last night's "Ab Aeterni" may have been the sneakiest, most confounding, but inevitably brilliant example of this groundbreaking show yet. Those who started watching this show this year were no doubt confused, but longtime Losties were richly rewarded, as the enigmatic and tortured Richard Alpert was transported back in time several centuries - and a few months - revisiting the very story he experienced in the previous version of this episode, "Ab Aeturno." (The difference in spelling is one those things that will be debated by Lost fans endlessly on the Internet.)

As we learned before, Richard was originally Ricardo, a poor Spanish fellow whose only joy in life was his wife, and whose life fell apart when his wife died of a complications of the plot. He sought to obtain medicine from a callous rich doctor who probably couldn't cure venison, let alone consumption, and in the process of getting the drug the doctor ended up dead. Co-pay this, senor. But this time we see the story, there were subtle differences.

The commercial that followed the deadly accident was for Wal-Mart, which recently abandoned its 70s-style (read: Dharma-project era) Smiley Face for a stylized sun. Yes, Sun, as in the wife of Jin. The previous time the episode aired, there was an ad for insurance. What does insurance do? It pays your survivors when you die. But Richard, as we now know, cannot die, so there's no point in him getting insurance. There never was. I think it's pretty obvious that since Richard's powers are diminished by his lack of faith in Jacob, he will be killed by Sun.

The episode showed the same grisly passage on the ship, and at first glance it seemed much like the original episode, but there were subtle differences. This time the screen displayed a message that said SPONGEBOB SQUAREPANTS IS ABOUT TO BEGIN RECORDING. YES / CANCEL

Now, flame if me if you want to, but I think this was an attempt to bring Spongebob into the Lost mythos. Hear me out. Where's the island in one of the alternate storylines? That's right: under the sea. Who lives in a pineapple? Spongebob. And the pineapple is where? Under the sea. Since the Black Rock ship (an obvious reference to CBS, which reportedly passed on the series, but that's another story) did not blow up in the alternate timeline, it is now under the sea.

Stay with me, because this is intense: what were the characters stuck in the 1970s timeline trying to do? Get back to the future. What was the name of the pivotal high-school dance in the movie "Back to the Future"? Enchantment Under the Sea.

You don't think they've been planning this all along?

So that's just a couple of things. The rest of the episode was full of subtle changes, except for the scene at the end where Jacob gives Richard some mascara. He tells him that he may be immortal, but he is not necessarily fabulous - which means this was a total head-fake.

I'm going to set up two TVs next to each other and watch both episodes simultaneously to pick up all the differences, and if I find anything else I'll write about it. From what I can glean, the ep was full of clues that are absolutely essential to understanding what happens next week. I feel sad for people who tuned in, thought "oh, crap, it's a repeat," and didn't watch. Well, there's always Hulu.