Chalchiuhtlicue, "Jade Skirt", is the goddess of lakes, rivers, and the sea. She's known for being the second wife of the rain god Tlaloc, and she's most commonly the Fourth Sun in the five sun legend.
Chalchiutlicue will often be depicted sitting on a throne with a stream of water flowing from her skirt.
Now, water looks like this in some Aztec codices. These are taken from Codex Mendoza, I was able to find these and the glyphs further down this post in the Visual Lexicon of Aztec Hieroglyphs online!
So water is parted like this, and it has these circle and tear-drop shaped shells on each end.
Here are some representations of Chalchiuhtlicue with water illustrated in the same way. Note that she also tends to have people swimming in there, and other objects.
I thought the strands of water looked similar to Us' tentacles from their bioship. They also use these tentacles to hold the others' ships in ep3, much like Chalchiuhtlicue has people inside her streams of water.
The way their limbs look in their physical form resembles the way the goddess' water flows, too
Another reference to water could be the design of Beebs' guitar. It has an ocean wave on it.
Beebs' god is Xipe Totec, and as far as I know he has no relation to the sea or water, but Us' does! The guitar belongs to Beebs, yes, but it's the fact that he uses it to communicate with Us, and the instrument becomes associated with Us, that it makes me think it's a reference to Chalchiuhtlicue, since she is the goddess of bodies of water.
Speaking of, in Beebs' post I said his guitar could be a reference to Xipe's rattlestaff, the chicahuaztli. This is an object that both Xipe and Chalchiuhtlicue can be seen carrying, along with a couple other gods.
Us makes a certain sound in Scratch's flashback, like that of a rattle (21:00) But it might be me going crazy.
I also considered Them to be designed to resemble a chicahuaztli, but that is a stretch, too.
Another important element of Chalchiuhtlicue's iconography is that she has a pair of tassels on the sides of her head, and her dress is also adorned with small tassels. This can be seen in codices as well as in statues of her.
Us has these drops of a black liquid beneath their cap, hanging by on the sides of their head. This is because they're based on an actual mushroom, the inky cap mushroom!
These drops could be a reference to the tassels perhaps?
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Next I wanna talk about this symbol on the cap of Us' bioship
This is an example of a quincunx, it's a geometric pattern consisting of five elements: four of them form a square, and the fifth one is placed in the middle.
Symbols like this one appear in monkey wrench, from subtle places like the dice in the casino
To the decorations in the bar and the restaurant, as well as the inside of Beebs' arm!
Why am I bringing this up? The Mexica used the quincunx a lot, in a variety of ways, but also with circles like we see in the show, so we're gonna focus on those here
They also used very similar circles for a couple of glyphs, such as these
I wanna bring attention to that fourth one. Chalchiuhtlicue's name consists of two words: chalchihuitl, "jade", and cueitl, "skirt". The symbol for jade looks the most similar to Us' eyes, with the texture of a jade in the middle.
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Lastly there is one more thing that Us and Chalchiuhtlicue have in common, thematically.
In the Legend Of The Suns, Chalchiuhtlicue is the Fourth Sun (although other versions exist). The way that her era ended was that Tezcatlipoca accused her of faking her love for humans to get praise. She cried for hundreds of years, flooding the whole world, and the humans that lived there turned into fish.
Us is the first and so far the only character to cry in the series, in a non-comical way. It's in this scene that the show takes a more serious tone.
Us is, arguably, a somber and sad character, especially after the loss of Them. Both Us and the goddess also seem to have strong reactions to their circumstances, seeing how Us was willing to join Them when they accepted that there was no help for their friend.
It is also worth mentioning that their bioship and their phantom form move like a jellyfish, like a sea creature.
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