When Veronica is in the library sorting the highlighters she has yellow and green markers in her hand and places the yellow ones into a box, keeping 4 green markers in her hand. Then Bonnie walks in and the camera goes away from Veronica and then back to her and in her hand she has 3 yellow markers and a green marker and there is also a yellow marker on the desk which wasn't there before the camera went off of her.
Veronica blames Madison for her being drugged, even though Madison had no way of knowing the drink was laced.