Some trivia I've noticed about FLCL
FLCL, a classic six-episode OVA series from Studio Gainax and director Kazuya Tsurumaki (known for his work on Evangelion), is well known for being kind of confusing. Its blistering fast pace, wild animation style, and total disdain for holding the viewer's hand makes it difficult to follow on a first viewing. But after watching the series maybe a dozen times, I finally think I mostly get what it's about, and even noticed a few cool things that I missed on my first viewings.
Spoilers ahead, so if you haven't already watched FLCL go do it now.
Japanese symbolism
Clearly coming of age is a major theme of the series, but just in case you didn't get that from the recurring sour drinks jokes the show literally spells it out for you.
The symbol that appears on Canti's and Naota's heads when they get possessed by Atomsk's power is made from the kanji for "adult" in Japanese (大人, literally "big" and "person"):
On the other hand, the symbol that appears on the Medical Mechanica giant hand after it acquires the completed terminal core is made from the kanji for "child" (usually 子, but can also be 小人, "small" and "person"):
Space Police Fraternity
Like Eva, there's a lot of cool lore going on in the background that you don't really have to pay attention to if you don't want to. The Space Police Fraternity it mentioned exactly twice in the series, and has no real relevance to the plot, but it's still a cool bit of trivia.
In episode 2 Haruko says her true identity is a "フラタニティの宇宙捜査官" (fraternity no uchū sōsa-kan, literally Fraternity Space Investigator).
This could probably be disregarded as another lie from her (she also claims to be a wandering housekeeper and a nurse), except that Commander Amarao brings it up again later in episode 4. While interrogating Naota he asks if he's heard of the 宇宙警察フラタニティ (Uchū keisatsu fraternity, literally Space Police Fraternity):
What's interesting is that the organization that protects humanity from space monsters in Tsurumaki's next series, Diebuster, is also called The Fraternity, also uses children whose brains can break the laws of physics, and also talks to its agents through cat telepathy. This reference would have been totally lost if you only watched the dub.
Director cameos
Although credited as "?", Naota's fat cat Miyu Miyu is actually voiced by Neon Genesis Evangelion director Hideaki Anno. Miyu Miyu never talks, but he does make wierd and hilarious cat noises. Anno would later go on to voice the protagonist of the 2013 Studio Ghibli film The Wind Rises.
In addition, the giant hand that reaches out for the Medical Mechanica iron is traced from a photograph of director Kazuya Tsurumaki.
Guitar continuity
Haruko's guitar, or "bat," is a blue Rickenbacker 4001, which has a pull cord like a chainsaw and also functions as a gun.
Haruko also uses a ukulele as a bat in episode 3 (causing it to break immediately), and Amarao's tiny guitar as a slingshot in episode 5.
Naota has a Gibson Flying V, which gets pulled out of his head in episode 4. It also has a pull cord, but Naota never uses it.
Atomsk's guitar, variously used by Canti and Naota (but never by Atomsk), is a 1961 Gibson EB-0.
In the final episode, Piratized Naota fights with both his guitar and Atomsk's, eventually fusing them together to form a cool double-necked version.
After the FLCLimax, Haruko flies away with the double guitar, leaving behind her own Rickenbacker for Naota. This is one of many cases where the sequels contradict the original story by having Haruko wield the Rickenbacker again, but we won't discuss those.
Other little things
In episode 4, the reason the satellite bomb got knocked out of orbit is because of the baseball Haruko hit into space in the intro of that episode.
The sequence in episode 5 where Haruko inexplicably wears a bunny suit and rides a flying guitar is a reference to the Daicon IV Opening Animation, Studio Gainax's first animated project.
Naota's dad, Kamon, is a bit of an otaku. In episode 2 Naota mentions that he wrote an Eva book a long time ago, and he references Initial D and Gundam among others throughout the series.
In episode 3 the Medical Mechanica robot comes out of Ninamori's head rather than Naota's. This is because when he collided with her after getting hit by Haruko's Vespa (again), there's a very brief moment at 08:57 where you can see the N.O. channel being transferred.
You have to start by swinging the bat
Every time I rewatch FLCL I notice something new, so I'm sure there's still stuff I missed in this densely packed series.