When Holden and Amos went into the Scopuli to inspect a distress call, only Amos brought a gun with him. You later learn that Holden couldn't bring himself to kill anybody, hence the lack of weapon.
The name of the shuttle being Knight is also quite fitting to Holden's personality.
Before Miller decide to leave Ceres for Eros, he saw a bird. More specifically, a bird that's flying in a rotating space station instead of normal atmosphere. It gave Miller an idea: adapt.
In the two-parter Season 1 finale, we are shown that water is leaking all over Eros station. Given how important water is as a resource to people in the Belt, this shows that the owners of Eros are up to something, since lack of maintenance on critical water infrastructure shows they intend to write the population off.
A cant is a dialect or secret language exclusive to a particular social-group. The Belter creole and hand gestures could be considered one. When Havelock tries to talk down the OPA rioters in their own language, they attack him anyway and tell him to "Remember the Cant."
Admittedly, in this case, "Remember the Cant" actually refers to the Canterbury, the ice hauler that got blown up, resulting in the increased water rationing that led to the riot.
In "Doors and Corners," Fred Johnson has the crew run simulations against one of the stealth ships. Where do they get the information that lets them do this against a ship that barely registers on sensors? From the CIC data recovered on the Donnager, that Johnson had cracked at the end of the last episode.
In "The Monster and the Rocket," Bobbie ends up on Jules-Pierre Mao's private luxury ship, and notices a tray of dainty cucumber sandwiches. She rushes straight over and gobbles them up — all of them. Yes, it's hilarious, but when you think about it, cucumbers are such a wasteful vegetable — they take a ton of water to grow, and aren't very nutritious. Since Mars has to be very economical with their agricultural output, cucumbers would be a rare treat. No wonder Bobbie does a beeline for them!
That's also likely why Mao provides them on his yacht—like the artwork and expensive furniture, inefficient luxury foods are another display of conspicuous wealth, even if a more subtle one.
The designs of the UNN and MCRN ships perfectly match their respective homeworlds: UNN ships are busy, weathered, and brightly because Earthers are used to bright light back home and also preside over an aging and numerically superior population. In contrast, MCRN ships are minimalist and dark yet futuristic because Martians are used to less light back home, live beneath a planet in harsh conditions requiring them to to be as pragmatic in design as possible, and have the most advanced technology in the solar system outside of maybeProtogen.
After seeing all the factionalism/infighting within the OPA last season, it's a bit odd to see Avasarala talk about them as if it's some sort of monolithic entity that has every Belter under its heel in "Assured Destruction". However, it makes sense since even with her being as politically savvy as she is, Avasarala still has her own cultural biases coloring the situation "out there" as an Earther politician. Additionally, Avasarala assuming that Naomi, as one of the "good" Belters, would not want to be associated with the OPA nicely showcases the UN's imperialist attitude towards the Belters.
In "Immolation," when Jules-Pierre Mao is brought before Avasarala and sees her, a very brief moment of terror and disbelief flashes across his face. She is wearing a Mao-Kwikowski flightsuit from the Razorback. The one that belonged to his daughter. So, From a Certain Point of View, both Julie and Avasarala are bringing him to justice for his crimes (however symbolically).
Most Belters have side shaves or mohawks, or otherwise very short hairstyles (the longest hair we see being Drummer's), whereas Avasarala practically has yards of hair. Which makes perfect sense, because out in the Belt, water is very limited—Belters can't afford to have a lot of hair because it would take up too much of their water rations to wash, whereas Avasarala, a rich and influential Earth politician, probably has access to as much water as she wants (or at least a lot more).
Having freely hanging long hair in zero gravity would also quickly become a liability with how easily it would get in your face with the slightest turn, or caught in any exposed machinery.
Ashford in Season 3 has extensive scarring on one side of his face, and based upon the way he walks, the rest of his body may be heavily damaged as well. He mentions while dressing down Diogo that he watched his only child burn to death. Given that Belter crews are family operations, there's strong odds that Ashford was burned in the same event that claimed his daughter (and likely while trying to save her as well).
Mars is the most advanced faction in the Solar System, with a highly automated economy. Yet, despite having a larger population than 21st-century Earth (which is suffering economic upheaval due to automation), Mars claims every citizen is a productive and contributing member of society and isn't tolerant of anything similar to Earth's welfare state. Considering Mars is also reliant on a sealed environment and food imports it won't tolerate unproductive individuals or extend a social safety net to those who struggle.
It's played as a joke when Amos tells Chrisjen that walking in mag boots is just like walking in pumps, simply replying to Chrisjen's and Bobby's confusion with "I didn't always work in space". But he also mentioned having grown up among prostitutes and implied having first hand knowledge of human trafficking.