The phrase "cracks open" refers to the act of breaking or splitting something apart, usually with force. There are several synonyms for this phrase that can be used in different contexts. For instance, "splits apart" can be used when referring to a physical object such as a piece of wood, while "bursts open" can be used to describe a container or a building. Other possible synonyms include "shatters," "ruptures," "severs," and "tears apart." Each of these words carries a somewhat different connotation, so it's important to choose the right one depending on the context and the tone of the sentence.