On a related note: In one episode, Damon walks in on Stefan and Elena after they've had sex. Both complain, having not gotten a chance to rest yet, to which he just says, "If I see anything I haven't seen before, I'll throw a dollar at it." At first, this looks like a nod to his ladykiller past/present, but then you pause for a moment. Stefan is his brother, which makes avoiding at least glimpses all but impossible, and Elena is literally a doppleganger of his ex-lover. Yes, he has genuinely seen it before. —Red Wren
When Tyler's car crashes due to the effects of the Gilbert Device, his eyes turn golden. Of course this is to forshadow that he has the werewolf gene, but it makes no sense as one has to kill someone (accident or not) to activate the curse. Then it hit this troper that Caroline was at that point dying of internal bleeding caused by the crash; in other words the curse was just on the edge of being fulfilled.
Or it just affects everybody that has the werewolf gene whether it's been activated or not, like with Tyler's father.
Seeing as we aren't getting a Christmas hiatus in Season 4 we have a higher chance of getting a holiday episode. Of course it's happiness level might be lower than the one Veronica Mars had.
Damon being the one to realize the sire bond in Tyler makes a lot more sense in Season 4, when it's revealed that he had a sired to him in 1940s
Stefan seemingly enters Caroline's house without an invitation in "Bad Moon Rising", but in "The Turning Point", Stefan rescues her from Logan and probably was invited in.
Katherine says that she had been taking vervain for 145 years in "Memory Lane". It seems to be just so she's not harmed by it, but in "Katerina" we learn that Originals can compel other vampires, so it also had the added bonus of protecting her.
In "History Repeating", Damon vows to drink animal blood, but nothing with feathers. Though seems like a simple joke, if you remember in "You're Undead to Me", Damon killed the crow that followed him around for sustenance. He had a good reason for not wanting anything feathered
In "We'll Always Have Bourbon Street", Damon meets a witch that doesn't practice anymore. In The Originals, we find out just why she doesn't practice anymore. It's punishable by death
Caroline's seeming ease controlling herself and her murderous urges once she becomes a vampire seem MarySueish at first, but it becomes brilliant when one remembers that becoming a vampire turned her into as she put it "insecure, neurotic control freak on crack". Basically she has a predisposition toward control including of herself that got turned Up to Eleven when she became a vampire.
Unlike in most media where vampires possess mind control powers, compulsion does not seem to particularly affect the mental faculties of those it controls unless the vampire using it specifies that the victim must not remember something or should think something in particular. This is later proven in "The Ties That Bind" when one of Klaus's Hybrids compels Jamie to shoot anyone who arrives at the house; while he sticks to the orders and attacks Stefan, he clearly does not understand why he is doing it. This means that others we have seen under compulsion, such as the man Isobel compelled to step in front of a car, resulting in his death were aware of what they were doing, but completely unable to control their bodies.
Which gives one an even darker perspective of Damon's "relationships" with Caroline and Andie.
Katerina's "turning" may qualify as this, and/or Fridge Tearjerker to explain: Katerina/Katherine ran-away from Klaus when Elijah told her about her about their plans to sacrifice her, and Rose walks in on her attempting suicide ( "I'd rather die than go back to Klaus ) and forces her blood into Katherine's system. When Trevor comes home, Rose ambushes him and scolds him for what he's done,and when they turn around to check on Katherine, she's hung herself. At first, one assumes that Katherine purposefully did this to turn herself into a vampire, but then you realize that Katerina had absolutely no way of knowing this. as she learned about Klaus (and, subsequently, vampires) from Elijah, but its highly doubtful that he told her all about turning and all that. Even though Katherine tells Elena that she had planned to become a vampire all along, all facts point to Katerina really having tried to kill herself, and her saying things like "You would have helped me run. That was never going to be enough" sounds like someone who had, originally, given up, and her saying "Better you die than I" sounds like someone who has been given a second chance at life. [[Tearjerker Which makes her personality change after turning that much more understandable]]
The show has recently revealed that blood sharing between vampires is considered very intimate with Julie Plec herself saying it's basically "vampire naked cuddling". Keeping this in mind, think back to Mikael's diet. It adds a whole new layer to the various vampires' obvious disgust towards it. It also adds to the reason why Damon was so opposed to Mikael feeding off him and why he had such a negative reaction to him feeding off Stefan. The guy just naked vampire cuddled his unconsenting younger brother right in front of him. And he did the same thing to Katherine as well.
When Elena and Jeremy kill Kol, Klaus angrily threatens to burn their house down. He's stopped from doing so, but I realized later this happens anyway, only with Elena doing the burning
Every supernatural death goes through the anchor. Amara was the anchor when Elena and Jeremy kill Kol. That created a WHOLE lot of supernatural deaths, all at once.
After Elena forces Katherine to take the cure, her body begins to catch up with all the years that it has been supernaturally alive, causing her body to start to age and decay. Katherine took the cure unwillingly, but remember who REALLY wanted it? Rebekah! If Rebakah had gotten her wish, imagine the fallout. Not only would she probably have died even faster, being more than twice Katherine's age, but the reactions of her brother's could have been... messy. Klaus is unstable enough with his siblings at least trying to keep him in check, and Elijah would have had the additional guilt of being the one to give her the cure.
Katherine only started aging after Silas drank her blood to get the cure for himself. It's a bit murky on the show, but I think we're supposed to assume that as long as the cure isn't passed on to someone else, rapid aging doesn't come along with it. Silas may have started aging if he'd lived much longer after Amara took the cure from him, but he wasn't technically a vampire and the cure was specifically formulated for his type of immortality, so it's possibly a side-effect only for former vampires who take the cure.
There's a scene at the end of "Graduation" where Silas takes on Elena's form. We later learn that his lover, Amara, was the Original doppelganger making the whole thing very squicky.
Every single werewolf has killed someone. At best, they have crippling guilt about the person they killed. At worst, they're cold blooded murderers.
Stefan's explanation of why Elena looks like Katherine. Apparently, he was only surprised by them having different last names, which could be easily accounted for by a female descendant of Katherine marrying a Gilbert, and not by the fact that people don't tend to look like their 150-years-ago ancestor's identical twin.
For the record Katherine is over 518 years old being turned in 1492. Before she was turned Katherine had an illegitimate daughter. It is highly likely that Elena is the descendant of that daughter so Katherine is Elena's perhaps 22 times great grandmother (assuming each generation is 21 years going back over 500 years).
In "A Few Good Men" Sheriff Forbes does a background check on Alaric and he has a clean record. However, in "1912" Meredith does another background check and finds several violent instances. How would the local law enforcement miss such things.
How did Elijah not realize that Elena was wearing his mother's necklace. The only way it could possibly make sense if he didn't know of it.
In "Isobel", Isobel says that she wishes her plan to plan to get Elena to stop looking for her had been more effective...except it was effective. Elena did stop looking. It was Alaric that didn't.