After Damon forces Elena to drink his blood the amount and position of the trickle of blood beside her mouth and on her chin changes between shots. The amount of blood seems to change but actually stays the same, the different camera angles show more and less blood throughout the scene. On the close-ups of Elana and Damon there is a small amount of blood running from her mouth, when the camera panes out you can see a larger amount of blood under her chin. When the camera is back to a close-up you cannot see under her chin, giving the illusion that the amount of blood is growing and shrinking in size.
During one of the 1864 flashbacks, a copy of Renoir's "Two Young Girls at the Piano" can be seen on the wall behind Katherine. This painting was painted in 1892.
During the 1864 flashback of Pearl getting captured, the compass only points to her even though her daughter, Anna, is only a few yards away watching alongside Emily. Considering that this is the last time Anna will see her mother for 145 years, the inference would be that Anna is already a Vampire. Also, as we later learn, Pearl is more than 500 years old (in modern time) and since vampires can't reproduce, Anna would have been a very old vampire even in 1864.