Parents need to know that "The Shallows" is a tense, bloody, jump-out-of-your-seat thriller starring Blake Lively as a young med school dropout who goes surfing at a secluded beach. After being chomped on by a shark, she must figure out how to survive and get to safety. Many scenes could scare the pants off of kids (and adults), including a shark jumping out of the water with its jaws open (then chomping down on a surfer) and a man crawling onto the beach with half his body chewed off.