Metaphor
Metaphor is one of the most fundamental figures of speech. Much of our everyday language is metaphorical in nature; we just don't always recognize the implicit comparisons that our most common expressions are making. A metaphor is a comparison of unlike things that seeks to identify the shared qualities of the things.

The critic I.A. Richards has provided a useful set of terms to describe the parts of a metaphor. The tenor is the "gist" or "point" of the metaphor, the phenomenon the metaphorical turn of phrase is trying to convey. The vehicle is the concept conveyed by the word or group of words that is used to make the explicit comparison.

The expression "leaping heart" is an example of a special kind of metaphorical language: anthropomorphism, the attribution of human (or at least animate) characteristics to non-human and inanimate things. The heart, which has no legs, is described as "leaping": the rapid heartbeat of the passionate Narcissus is compared to a person (or some animate creature, perhaps a frog) jumping up and down.