While Marissa and Luke are talking at the Crab Shack on a table, Ryan and Donnie are talking at the bar by the register. When the camera focuses on Marissa and Luke, the spot where Ryan and Donnie are talking, can be seen behind Luke, but there's no sign of Ryan nor Donnie, until the camera focuses again on them.
In the scene after Ryan and Marissa jump in the pool, they both go to the pool house to dry off. Ryan is drying off Marissa and some of her hair can be seen hanging in front of her face. In the next shot it is brushed back behind her ear, then in her face again and back to being brushed behind her ear, continuing on between the two shots.