As the song goes, time kept on slipping in last night's episode of Fringe. What was behind it? That would be telling... but even that wouldn't answer all of our five questions about "And Those We've Left Behind."

Is Time Malleable?

Something that stood out to me about Raymond's time bubble, especially considering the way this episode ended: He kept going back and changing the past, and yet the future was never impacted. Sure, during the periods where he'd be running the time bubble, there would be effects elsewhere, but they'd disappear as soon as the time bubble shut down. But he actively changed Kate's history, and yet nothing changed beyond the notebook being scrubbed in the present. I can't work out if this is just lazy writing or something else; considering the amount of time travel and, more importantly, time being rewritten that we've seen in the series so far, if it is lazy writing, it seems to have come out of nowhere. So is it a clue to something we don't understand yet?

Were Kate and Raymond Analogous to Peter and Walter?

Raymond abused science and messed with forces that he didn't understand to save the person he loved, with disastrous consequences; as we know from the last season of the show, that's exactly what happened to the Walter who crossed universes to save (a) Peter. Sometimes, Fringe seems like the most pessimistic show on television. But it's interesting to revisit the idea of the scientist who'll do anything for love - Sorry, Meatloaf - at a time when Walter would rather shut out Peter altogether ("The Subject"? Even worse, "it"?) than engage emotionally. Are we supposed to take it that "good" scientists ignore their emotions for the good of the world, this time around? If so, see what I said about the show seeming like the most pessimistic show on television.

Why Did Peter Appear To Olivia and Walter?

The discovery that Peter didn't remember appearing to Walter or Olivia before his return was surprising, and just brings up all manner of questions: Was that the same Peter (Is there another Peter?), and if so, why can't he remember doing that? Or does he remember, and he's lying for some reason? What if it's a future Peter, trying to stop himself from coming back? And so on... But, talking about revelations that came out of nowhere...

Is Peter Trapped In Another Parallel Earth?

"Maybe it's not time that needs to be reset. Maybe it's me." The sudden, surprising suggestion that it's "our" Peter, but that he's on another parallel Earth is a massive one for the mythology of the show. It's not that the idea of infinite parallel Earths hasn't been raised before, but if this is the case, then it suggests that everything we've been watching all season has been like the "Over There" episodes last season... Something that "counts," but isn't necessarily the same show as the one we normally watch. Suddenly, I become suspicious of the opening titles, and the way that they've been amber since the season started. Last time they changed color, it was to suggest that we weren't in "our" world, but another one altogether. Have we been getting clues all along about this? And if this is a parallel Earth, will we ever see the one that the show started on ever again?

Was That The Worst Product Placement We've Seen Yet On Fringe?

Fringe has had some terribly obvious product placement in the past - Wasn't there an awkward scene where Olivia and Peter talked about how great their car was, once, or am I imagining that? - but Lincoln's "You need to see this, oh please let me show off how great Sprint's video phone is" moment was... weirdly patronizing, really, and something that stood out like a sore thumb during what should've been a much more exciting moment. It was, in its way, a perfect summation of this entire episode; something that should've been better, but, somehow, just wasn't. Or am I the only one who was disappointed with what we saw last night?