In the Season 5 finale, we finally learn that, by detonating Jughead, the Lostaways themselves may be responsible for the much-discussed "incident" of the island's history. Whether Jughead literally reset time, as Daniel Faraday said it would, remains to be seen.

In Season 4, Claire survived an explosion in New Otherton only to wander off into the jungle in the middle of the night, leaving Aaron in Sawyer's care. When we last saw her, she was with Christian Shepherd, her father, in Jacob's cabin. Is Claire dead? We'll find out. Emilie de Ravin returns for Season 6.

In the Season 5 finale, Man No. 2 (in the guise of John Locke) killed Jacob, the spiritual leader of the Others. He's been on the island at least as far back as the arrival of the Black Rock.

It's been described as a security system. It appears to show people scenes from their lives. It has taken the form of others (Yemi, Alex, possibly Christian Shephard). It has also killed people.

For four seasons, a battle between Benjamin Linus and Charles Widmore established no clear bad guy. Both were kind of creepy. Now that we've met Jacob and Man No. 2, we wonder, yet again, who we should trust.

Hurley had extremely bad luck after playing 4, 8, 15, 16, 23 and 42 in the lottery after overhearing them at the mental hospital. Desmond's lack of entering them into a computer caused Oceanic 815 to crash. They've shown up everywhere. Is there some larger significance to them?

Mystery has surrounded Claire's son Aaron even before he was born. A psychic told her she, and not adoptive parents, had to raise her unborn child, but then encouraged her to give the baby to a couple in Los Angeles. The Others seem awfully interested in Aaron as well. Is he a miracle baby? A harbinger of doom?

An old wooden slave ship called the Black Rock sits almost dead center on the island. After he left the island, Charles Widmore purchased a painting of the ship — and its logs. In the Season 5 finale, Jacob and Man No. 2 watched a ship that appeared to be the Black Rock sail toward the island.

Juliet was brought to the island specifically because of her previous work with fertility treatments. However, even she couldn't stop the mysterious immune problem on the island. How and why expectant mothers' bodies "turn on the fetus," as Juliet says — and always during the second trimester — has yet to be revealed.

Kate and Jack discovered a pair of skeletons in the caves in Season 1. Locke dubbed them Adam and Eve. The producers have hinted that their existence would prove that they had an endgame in mind from the beginning.

Danielle believes the whispers are the Others. We think it has something to do with time travel. All we know for sure is that they're usually a sign that something bad is about to happen. Shannon heard them before she was shot and killed. Jack, Kate, Sawyer, Hurley and Michael heard them just before they were ambushed.

When the Oceanic 6 (minus Aaron) returned to the island in Season 5, four of them ended up back on the island in 1977, where they reunited with Sawyer, Juliet, Miles and Jin. But Sun ended up on the island in 2007. Why? What makes her different from the others?

Richard Alpert looks identical in scenes that take place in 1954 and 2007.

In the Season 5 finale, we see that Jacob visited Kate, Sawyer, Jack, Sayid, Jin and Sun and Hurley before they all boarded the same doomed flight. Why were they so special?