Continuity mistake: When Marissa leaves the bar, after downing the pills and tequila, she leaves her bag, but presumably Ryan found it. Then, when Ryan sees Marissa down the alley he runs to her, but his hands are empty, yet, in the next shot, where he kneels over her body, Marissa's bag is in his hand and he puts it down beside her.
Continuity mistake: After Summer calls Seth and Ryan from the bathroom to say she's found Marissa, she puts her phone on the shelf, and then goes back into the main room to find Marissa gone. Then as Summer walks out the door she shoves her phone back into her bag, even though she left it on the shelf.
Continuity mistake: At the beginning of the episode when Seth is eating in the Crab Shack and talking to Ryan, he's holding his drink but in the behind shot he's bringing the drink to his mouth but in the front shot it's resting on the bench and again in the back shot he's sipping the drink but in the front shot it's nowhere near his mouth.