More specifically, we want to talk about Aria's (Lucy Hale) "hallucination" of Alison (Sasha Pieterse) — and, most notably, Ali's parting line, "You know why I picked you, right?"
That enigmatic line is one of showrunner Marlene King's favorites from the episode, and we can't help but wonder what the heck it means. While we're unlikely to get a real explanation any time soon, at least we can speculate, right?
Here are a couple of theories about what Ali "picked" Aria for.
To be part of the group. Maybe this was an enigmatic reference to why Ali brought Aria under her wing. Did Ali make Aria part of the group for a reason that relates to "A" and/or the mystery of how she died? To appear to. Maybe she was talking about why she appeared to Aria right then — perhaps because she was in danger. Ali does seem to show up to each Little Liar in a time of need.
To be part of the "A" team. This one is more out there, but some fans love the theory that Aria is part of the "A" team. If this theory is true, perhaps Ali is the one who recruited her, and she was saying "You know why I picked you to be part of the team, right?" Hey, just a thought!