When Damon Salvatore chases Caroline Forbes up the basement stairs after she lets him out of the cell, there is a bright light shining at the bottom of the steps even though the basement was dark in the previous scenes.
When Elena wakes up and reaches for her diary, one shot shows her vervain necklace hidden under her hair on her right, but the next shot shows the necklace in the middle of her chest. The next few shots alternatively show the necklace in the two positions.
When Bonnie sets the car on fire, the first couple of shots of "Bonnie's" back are obviously a stand-in and not Kat Graham. The stand in has much wider shoulders, is much more muscular, has longer and more curly hair, and does not have the birth mark that Kat Graham has on her back in later shots.