Vampire fangs don't grow back. This makes sense if vampires developed from humans since teeth are one of the few things that humans don't grow back either. You get your baby teeth and your adult teeth and that's it. Fridge Logic at the same time though since the fangs are obviously not as prominent when the vampires aren't vamping out so where they go is a question.
Josh, in werewolf form, instantly stopping raging and lying next to Nora along with other information we've been given suggests some information on the whole thing. That the wolf is actually pretty intelligent and such but given that it's essentially starving and trapped for the majority of it's time. So when it gets loose, it has really only one thing it desperately wants. But give it something to focus on and it has bigger things to worry about than starving. It also explains why werewolves would attack their human family - they're not family to the wolf since the wolf was born 'after' and has no personal connection of pack or mate.
On the flip side, this would also explain why Nora's wolf distinctly remembers her abusive ex to the point of urging her to hunt him down. Their wolves are definitely intelligent enough to remember things but don't really have the mental facilities to really express themselves. For the average werewolf who is probably filled with a general sense of self-loathing, the wolf might express this as "If I kill 'em all, then I don't have to worry about hiding!"
Why does Aidan - a guy who is shown to be kinda hesitant on forming close relationships - have such a strong one to/towards Sally perhaps more so than Josh? Josh, it makes sense - they both want to be normal (or what have you). But Sally can't exactly stop being dead (well, mostly). When you consider that Sally could - theoretically - exist as long as Aidan would, then knowingly or not, Aidan's probably so overly protectively of her since she's one of the few people he 1) likes and has a relationship with and 2) will never leave him through/by time, death, or the majority of vampire politics.
Nora's miscarriage is of course for the drama but there may be some in-universe justification if her abusive ex (the one who mutilated her stomach) did enough harm to damage her reproductive organs to cause higher risks in pregnancy.
I think the miscarriage was meant to have been caused by the baby being a werewolf and its mother being a human — note Nora miscarried at roughly the same time as/not very long after Josh began to transform.
Aidan's plot with Henry is supposed to mirror Josh's plot with Nora. The parent who denies their monstrous side gets into conflict with their child who revels in it.
The US version of Being Human (which is a sightly newer and updated remake of the British version) takes place in Boston, a city in a region known as New England.
Bishop has a system in place that explicitly allows vampires to drink live blood from willing donors without having to kill or worry about maintaining the masquerade. Considering that option, Aiden's rejection looks like it really is more about his anger at Bishop and trying to PRETEND he's human than about trying not to kill or hurt people.
When he goes on a grief-induced binge, the vamp-bouncers even forcibly restrain him from actually killing one of the girls in his bloodlust (Rebecca certainly would have appreciated having someone like that around in the first episode).
Of course, as mentioned above with Bishop, this system is less about protecting the humans and more about practicalities of being a vampire. If you kill one willing donor, it makes it harder for more donors to step up. And of course, it's probably a given that the donors aren't aware of his more... dubious coverups and activities.
Of course, it also means dealing with Bishop, something Aidan is actively trying to avoid.
Probably comes down to Artistic License Biology, but the flu does not linger in a population the way people think the vampire-killing flu does. People get sick, they fight the infection, it clears their system and goes away. When enough people do this, the disease burns out of the population until a new strain mutates and does it again. Logically, then, it can't be the flu that's killing vampires. What does remain afterwords, though? The antibodies. Therefore, it must be the antibodies in the blood that kill vampires, not the flu itself. This is important because antibodies can be tested for (easily if somebody's manufacturing test kits) and the white blood cells that carry them can be filtered out of the blood. A doctor, a nurse and a genius medical student, you'd think somebody would've figured this one out by now. But they have been distracted and Nora's probably not so motivated to find a solution.
This is actually accurate. Aidan points out in one episode that it is in fact the left over antibodies that do the killing.
This also (may) explains why werewolf blood is a cure. It might not be anything inherent to werewolf blood that does the trick but more the fact that drinking werewolf blood causes a vampire to eject any and all blood in their system... which would also flush out the anti-bodies.
In a world where vampires and ghosts can hijack your brain, how can someone who knows this be sure that anything they've done, seen, or experienced is really what happened?
Nora's initial attachment to Josh despite his odd and distant behavior? Her unwillingness to confront Josh about her scratch? Being that she's the victim of abuse, it may have been that she was falling into old behavior - it's only as Josh really makes honest attempts and doesn't shut her out that she starts reacting and acting towards her situation and is able to confront him. This is probably why Josh was so caught off guard when she finally got angry. So when she finally confronts Josh and he doesn't abuse her, she's caught off guard.
This also explains Nora coming back and the methods by which she tries to make amends. It is in part the abused side of her.
When they threaten Nora, Josh turns into a wolf and kills the Boston Pack, which is implied to consist of every werewolf in New York and possibly the world. While his wolf's anger was justified, it's quite possible that Josh just singlehandedly drove werewolves extinct.
Made a little more hopeful considering that Josh and Nora have children in the epilogue, meaning the werewolves could be repopulated. And, assuming they've inherited either Josh's enhanced lycanthropy or Nora's bond with her wolf form, they'll probably be much more likely to stay alive than the previous generation of werewolves.
Fridge Brilliance/Fridge Logic: Where does the strong connection between sire and child come from and how did Bishop (and other leaders) cultivate loyalty in their followers before they were vampires? Sure, wining and dining and such, but eventually the topic of "So... you wanna be a vampire?" has to come up for it to happen. The answer may very well be... their mind control ability! They slowly cultivate not just an actual social connection but subtle influence someone until they're ready. And once turned, between the bloodlust and politics, the new vamp isn't likely to go back and question how they got there.
Brilliance and Horror with maybe a touch of Foreshadowing: Remember Stevie's Limbo death? It's by hanging. He even mentions that it's not actually how he died (he ODed on pills). Well... how does he die the second time? Yup, by hanging.