Bob up is a verb that means to arise suddenly or unexpectedly. There are several synonyms for this phrase, including pop up, surface, appear, emerge, and come into view. Other phrases that have a similar meaning to bob up are crop up, show up, come up, and present itself. These synonyms can be used interchangeably in many different situations to describe things that suddenly come into view, such as a whale bobbing up from the ocean or an idea suddenly occurring to someone. Using synonyms like these can add variety and interest to your writing, making it more engaging and memorable.