It's the time travel thing. There's something that's bugging me.
See, at the beginning of the episode we have Barry watch an image of himself running a lot faster (let's call this image, Barry') what causes him to stop, take a look around, and then proceed to the morgue. So far, so good. Then, at the end of the episode, in order to save the city from a tsunami, Barry runs so fast he actually travels back in time and encounters an image of himself running but a lot slower (let's call this image, Barry''). We all got the gist of it; Barry' is supposed to be Barry at the end of the episode (future Barry) and Barry'' is Barry at the beginning (past Barry). No problem here either.
What puzzles me is that, at the end of the episode, Barry stops and takes a look around like he did at the beginning and watches the same events unfold (dogs barking; guy spinning sign; woman trying to hail a cab). In a (classic) time loop, Barry'' would've been the one to stop and watch these events unfold, not Barry. The fact that it's Barry who now does this tells me he has altered the timeline, even if in a small way. After all, no two Barrys can be at the same place, at the same time, watching the same events unfold. In other words, the timeline Barry' flashed into turned out to be different than the one he came from, and so is now the timeline Barry has flashed into. It's not exactly a time loop but more like a tree that branches out from a common starting point.
Anyway, now we have two Flashes in the same timeline. In fact, we had Barry and Barry' for the majority of the episode and now we have Barry and Barry''. I'm curious to know what Barry' was doing in this episode and how that will match up to what Barry does in the next one. I'm assuming Barry will have to return to the future (of Barry'') what could be an interesting setup given the fact the Reverse Flash is so eager to return to the future.
Oh, there's another thing with Harrison's explanation about killing Barry but it'll have to wait until tomorrow 'cause it's late.