I did already make a post about this, somewhat, but a lovely friend of mine (@beloved-cat-gremlin, thanks Anny đ) informed me off the 16 pages of notes Andy Weir wrote on Eridian biology, so ofc I was all up in and around that shit, and after reading it I wanted to delve into my headcanons about Eridians a little more and expand on them too given the added knowledge I have about their biology now (esp since Andy didnât go super in depth on Eridian culture/emotions/body language etc, so Iâve taken it upon myself to develop that aspect of their species. Heâs basically given me free reign <- deranged), so HERE WE GO
Iâll start off with one thatâs already pretty popular; Eridians can purr! It sounds WAY different from how Earth cats purr tho, itâs a much lower frequency and more of a continuous rumble rather than breathy purrs. Although, similarly to Earth cats, Eridians can control the pitch/volume/intensity of their purrs. The specific frequency of an Eridianâs purr also depends on their size - Rockyâs purring is probably closer to that of a cheetah or cougar (did you know they can purr?! You do now!!), whereas Adrianâs would be much lower pitched. Eridians can also continue talking while purring.
Eridians can be twins! This one is also at least partially courtesy of Anny, as she put the idea in my head (hi again bestie đ€). Twin eggs are also typically genetic, meaning an Eridian who is a twin is very likely to have twins themself when they have pebbles of their own. Since Eridian eggs are basically a jumbled up soup of competing genetic information, sometimes the competition gets so intense that two separate embryos form, that are often identical. These ultra-competitive genes are usually what causes twinning, however the genes from the parent with the twin-gene typically donât win, and the twins end up looking more like their other parent while the aggressive-twinning-gene stays dormant.
Eridians âcryâ and âscreamâ by emitting a high-pitched wailing sound called keening. Eridians often keen when distressed but will also sometimes do it when overwhelmed with joy. Keening also sounds like a kettle boiling, ironically.
Eridians can also have panic attacks, but they work very differently from a human panic attack. When an Eridian panics, muscles in their carapace cause their vents to slam shut as tightly as possible, making breathing nearly impossible. Since Eridians breathe to regulate their body temperature, panic attacks pose a much greater threat to their physical health than they do to humans, as it only takes a few minutes for an Eridian to start to overheat. Thankfully the average panic attack only lasts about three minutes before their vents split open again, but they can be continuous and hit an Eridian in chains or waves, which is why itâs important for them to seek grounding or calming techniques before hyperthermia sets in.
Despite having little to no feeling in their outer shells, Eridians can be ticklish! The most common sensitive spots are around the mouths on their undersides and their vents, as these are both vulnerable areas. Rather than scribbles, gentle tapping or vibrations are what cause the sensation of tickling. Pebbles are generally more ticklish than adult Eridians, since their shells are thinner and not fully hardened yet - itâs theorized that Eridians evolved this sensitivity as a form of play to teach pebbles to protect their sensitive shells from damage. Eridian tickle fights generally involve pressing their carapaces as close together as they possibly can and purring as loudly as possible - the deeper the vibrations can penetrate, the more it tickles.
Eridians have pet names! Most languages have their own equivalents of words like âdarlingâ and âdearâ, but other terms of endearment translate to things like âmy songâ, âmy star/sâ, âmy sun/sâ, and âmy [partnerâs name]â. Since sound is such a key component of their culture, they can get very sappy and lovey-dovey when talking to each other (think Anakinâs iconic monologue to PadmĂ© in the fireplace scene in AOTC, thatâs how Eridian partners talk to each other all the time).
Despite Rocky not being aware of what a hug is, Eridians cuddle! Typically Eridian cuddling involves squishing in really close to each other, and sometimes wrapping their arms around each other - the more arms are involved, the closer the relationship is. Generally Eridian âhuggingâ is more like spooning. Part of the reason Rocky was so surprised when Ryland tried to hug him the first time is because he was internally going âoh. Oh?! Oh!! Weâre THAT close now?!! Oh okay-â. Also he was a tiny bit freaked out by Rylandâs big gangly arms around him, because again, typically arms arenât involved in Eridian cuddling as much as just being physically close to each other. This type of affection is also pretty much solely reserved for families. The first âhugâ scene was the moment Rocky realized Ryland considered him family đ„șđ„ș
Other common forms of physical affection for Eridians include tapping or caressing each otherâs hands/arms (this is like holding hands or a more casual hug for them) or stroking each otherâs vents (which is often used to soothe a distressed Eridian - especially since gentle caressing can encourage vents that have slammed shut during a panic attack to reopen)
The awkward fiddling and fidgeting Rocky does with his hands throughout the movie are a common nervous habit for Eridians. Itâs equivalent to a human biting their nails/lips (though it does way less physical damage)
Solitude is even worse for Eridians than it is for humans. Their culture is even more centred on socialization than human culture, with most aspects of their lives intended to be communal. Being alone for extended periods of time is often severely detrimental to their physical and mental health, and reintegration can wind up being even more damaging due to the shock
Eridians have their own form of blushing! Itâs very different from how humans blush, ofc, since their blood canât be seen through their shells. Instead, when Eridians are embarrassed or flustered, their vents steam, and slightly hotter/more vapourous air comes out of them. Basically, they turn into living mugs of fresh, hot coffee when theyâre embarrassed đ€ this is also an Eridianâs way of sweating
Eridians also make an annoyed sound called a âwhuffâ, which is just a very loud exhalation from their vents - think a very dramatic sigh in a human and thatâs pretty close lol
Eridians can get âgiggle drunkâ! Laughing a lot for an extended period of time can make them sluggish/sleepy, and itâs honestly fucking adorable. They stumble around and their legs get shaky, and they usually have to sit down until they can get themselves pulled together
Due to their extremely sensitive hearing, Eridians hate loud noises. But this is also because overwhelmingly loud noises functionally âblindâ them, as they canât echolocate when a much louder noise overtakes their ability to hear
Despite not even being able to detect it, Eridians are bioluminescent! Itâs a slight, faint glow that only comes from certain patches on their body, and presumably happens because some of the minerals that form their shells glow in the dark.
Eridian families are extremely close-knit. Pebbles often know their parentsâ siblings, grandparents, grandparentsâ siblings, and cousins EXTREMELY well. Big extended family gatherings are practically their way of living, and the idea of a âfamily unitâ with only the parents and kids seems odd to them.
Eridians âshrugâ by giving their carapaces little wobbles. They basically do a little âidkâ dance đ€
Sometimes pebbles can come out looking absolutely nothing like either of their parents - color-wise. This is something Eridians typically canât pick up on, but Ryland, as a human who can see colors, was definitely a little concerned when Rocky and Adrianâs pebbles hatched and one of them was pale pink, not clay brown or turquoise-y blue like their parents. Since Eridians donât really rely on physical appearance outside of shape, genes just never really evolved to be super consistent with shell color/texture, so sometimes completely random genes pop up from a couple generations ago (one of Rockyâs parents is a pinkish-white color, so that alleviated Rylandâs anxiety - now he just jokes that Rockyâs genes put up so little of a fight that his parentsâ genes had to take over đ€Łđ€Ł)
A pebbleâs shell is extremely delicate up until their fifth-ish molt, so in that phase protecting them is crucial, as a crushed or cracked shell can, obviously, be fatal. It only takes about one Eridian year for a pebble to reach five molts, and in that time the little ones usually ride around on their parentsâ backs for safety, kinda like how some spiders and scorpions do on Earth
Eridians donât need ultrasounds, since they can âseeâ through the shells of their eggs. However Eridians will periodically check the development of the pebbles inside their eggs by echolocating.
{slightly nsfw warning!} Eridians do have their own version of sex that stimulates the laying of eggs better. Two Eridians will press their orifices together and generate a much lower frequency type of purr, which is only used for mating (and sometimes foreplay). Certain parts of the orifice are jam-packed with nerve endings that create intense feelings of pleasure when stimulated like this. Mating like this only takes a few minutes, but Eridian couples (especially ones that are actively trying to have pebbles) will often repeat the process up to ten times to get a full clutch of eggs, which are formed between their bodies during the mating process and placed into a nest when they separate. Thereâs not a wide variety of sexual positions Eridians can do, but the most common ones are the two laying on their sides next to each other with their legs wrapped around each other to keep themselves in place (Eridian missionary if you will), or one partner rolling over on their back with their legs splayed out while the other gets on top - which can be somewhat more dangerous, as it can cause the partner on the bottom to overheat, but for some Eridians, thatâs part of the eroticism.