The phrase "pounces upon" refers to when an animal or person suddenly moves quickly to attack or capture something. There are several synonyms for this phrase that can be used to add variety and interest to your writing. Some of these synonyms include jumps on, lunges at, attacks, strikes, seizes, assails, tackles, ambushes, and swoops down on. Each of these synonyms describes the act of attacking or capturing something with sudden and aggressive movements. By using these synonyms, writers can create more dynamic and engaging prose that captures their readers' attention and keeps them invested in the action.