Slice of Life/Mysteries and ciphers

There are many mysteries (some still unsolved) scattered throughout the series, most in Season 5.

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A mix of different ciphers, the code was solved in 2016, and appeared on a shirt in Pie's closet in episode 2. Fans have figured out that it uses ROT13, Vigenere, and Atbash, but could not find any keywords anywhere in the series, until 2016 when one dedicated fan reportedly frame-by-framed episode 2 and found random letters flash onto the screen for one frame. At first he suspected another cipher, but quickly realised that it was a keyword. He reported it to the shows Subreddit, and within days the code was revealed to say "piewillsurrendercookiewillrule". A nice foreshadowing.