Having established the geography of the beach with fluid tracking shots, Spielberg adopts a series of quick cuts that set up a number of bathers as potential shark food. The first - a POV from Brody's perspective - is a medium shot of the overweight lady floating on her back. The young man with the lemon polo shirt runs across the frame from left to right, obscuring the view, and then we cut to a medium close up as he throws the stick for his dog. This, and the following shots that are all seen from varying low angles, are clearly not intended to be showing what Brody is seeing. In pursuit of the stick the dog races into the water, where a young couple is canoodling in the shallows. There is another cut to Mrs Kintner in profile as Alex runs past her with his raft, and this is followed by another low angle shot as the boy launches himself onto the ocean. With each shot the camera has become closer to the water so that as viewers we almost feel as if we are in it as well. The next shot is of the dog swimming with the stick in his mouth and being intercepted by a male bather. Then we cut back to the overweight lady, still kept afloat by her bulk and slowly turning in a clockwise direction. Another cut to Alex on his raft, propelling himself with kicks of his legs and a two-armed paddle stroke. The images are accompanied by the sound of splashing and water activity.
The next cut returns us to dry land with a medium shot looking along the beach from a reverse angle to the establishing one. A song on the radio provides ambient background music. The beach - a crescent of white sand - is almost deserted and the most conspicuous items on it are two more empty lifeguard stations. The boy and his dog are having a playful tug-of-war. There is a travelling shot of the dog prancing in surf, and then we cut to a medium shot of Brody. He has shifted his position to one side of his chair and leans his right elbow over the back of the metal frame. His hands are clasped - just as they will later be in the dinner table scene with his son - and his right leg is crossed in a manly fashion over his left. His posture suggests something between relaxation and attentiveness. It is almost as if he is literally on the edge of his seat, waiting for something to happen.
Abandoning the rapid cutting technique, Spielberg now moves from shot to shot with clever imitation wipes. A bather passes in front of the camera, briefly obscuring our view of the watchful police chief. As the bather moves out of the frame we are aware that the shot has moved in closer. Another passer-by wipes the screen and we move even closer. The combination of the 'wipe' and the cut create a single fluid image. Compare this scene to Mrs Brenner's discovery of the eyeless corpse in The Birds where Hitchcock creates a jarring effect by cutting closer on the same image. In Frenzy the same director used an imitation wipe to cheat in the creation of a long travelling shot: watch for the moment when the Covent Garden porter passes across the frame with a sack of potatoes, seamlessly joining together studio and location work.
In the grammar of film a cut can be used within scenes or to move from scene to scene. Traditionally, a fade or dissolve is used to indicate the passing of time and as such is rarely used within a single scene (although, off the top of my head, I can think of examples in Citizen Kane and Taxi Driver). A wipe is most frequently used to indicate both a change of time and location, or - in this beach scene- as a sleight of hand, like some of the camera tricks of Georges Melies. Like the Iris-in and Iris-out of the silents, the wipe has become rare in modern cinema unless it is being used in a post-modernist ironic way, or - as in the Star Wars movies - as a kind of retro throwback.
Spielberg uses cuts when he allows us to be the observer of the action and 'wipes' when he wants us to watch it through Brody's eyes. The contrast of the staccato rhythm of the former and the perceived fluidity of the latter helps to create a kinetic tension that builds to the 'Vertigo moment' when the screen seems to expand and contract at the same time.