Ciaphas Cain/Fridge

Fridge Brilliance

 * Both literally and metaphorically, in that the Valhallan infantry Cain serves with in the first three books and Duty Calls are assigned to bases in cold, snowy environments three out of four times...which is just like home for them and frequently serves them in good stead. Also, it might go unnoticed on a first reading of The Traitor's Hand that
 * Here's a great one, if you can spot it: In every novel that is set chronologically after Death Or Glory, Jurgen goes out of his way to always make sure that Cain has tanna tea at the ready (even going so far as to catch up with a strike team that Cain was leading that was about to leave without him). Why? During Death Or Glory, it's a running gag that Cain keeps wishing that he had some tanna available, continuously asking whether anyone they meet has any, even making a joke, in Jurgen's presence, that the only cup of tanna on the planet is on the other side of a massive army of Orks, and Cain was just about thirsty enough to go after it. Now, put this together with the fact that Jurgen is EXTREMELY literal-minded, and almost never recognizes a joke when he hears it. The reason why Jurgen supplies Cain with tanna at all times is now clear: Jurgen genuinely believes that Cain loves tanna so much that he would fight through an army of Orks (or anything else, really) for one cup.
 * How about this: tanna is an actual drug. Not like heroin, probably something closer to alcohol or marijuana - not physically addicitve, but very psychologically addictive. This is why Valhallans have time to make it during battles. This is why Cain was actually willing to fight through a continent full of orks to get some precious leaves - abstinence, ladies and gentlemen.
 * It's tea. Valhallans are Space Russians. Russians love to drink tea. Yeah.
 * It's mentioned many times how people recoil from Jurgen, sometimes without even noticing that he's there. Cain attributes this to Jurgen's appalling lack of personal hygiene, but the 40K fluff describes blanks as creating exactly this reaction in others, which means that Jurgen's unwashed nature is likely deliberate on his part, to provide an obvious source of discomfort to hide this.
 * Likely Jurgen isn't even consciously aware that he's a blank. Think about it. The Warp is the manifestation of sentient being's emotions, hopes and dreams, fears and nightmares, all of it. Sentients, humans in particular, are able to come together and pool resources and power to a greater end because they can form social bonds through Empathy. We know a Blank is very dangerous to a Psyker because they cancel out their flashy warp powers, but what if it doesn't stop there, what if it goes all the way down to the basic levels of empathy that allow others to socially interact? What if that works both ways? Jurgen doesn't bother keeping himself clean, or well-groomed, or keeping his porn-slates hidden because he honestly can't see why any of that should matter.
 * Cain at one point says that his memoirs are essentially elaborate confessionals. Here's a tip: if you describe yourself as an awesome person during a confession, you're doing it wrong.
 * Why does Jurgen treat Cain like that? Everyone hates blanks, right? He was very likely a Butt Monkey since birth, assigning him to each other is a practical joke amongst the CO of 12th Regiment. He is stuck in the lowest military rank possible despite being potentially a great driver or a quartermaster officer. Then comes Cain, an infinitely superior officer, and treats him like an actual human being. And then risks his life saving him despite not even knowing the guy. And then treats him with genuine respect when he's assigned to be his personal aide - poor guy was surprised as if Emperor himself gave him a handshake. Remember the old principles of "I owe you my life", add Valhallans' honour code, which is likely as strict as that of Vikings and Russians, and there we go.
 * What further proves this theory is the fact that Jurgen never flinches despite facing Necrons, Tyrannids and Orcs. The only time panic is ever described is when Cain himself is either in danger or may be dead.