A metaphor is figure or speech used to express a comparison between two things. For instance, "His face was blank; his movements mechanical and precise," is a metaphor that indicates the subject's face is expressionless, not literally without features. The subclause amplifies this impression.
The metaphor "Her fingers danced and leapt across the warp and weft of the loom," suggests that the woman is a skilled weaver, not that her fingers actually danced or jumped into the air. Similarly, "When the volcano erupted, the mountain lake became a bubbling cauldron," clearly doesn't mean that the lake became a pot on a fire. Rather, the methaphor provides an image of how the lake looked when it was subjected to the volcano's heat. "Jim has a short fuse," warns that Jim is prone to sudden explosions of anger.