Here's why:
* Metaphor: A figure of speech where a word or phrase is applied to an object or action to which it is not literally applicable. It creates a comparison without using words like "like" or "as."
* In this case: The jeweler is not literally a vulture, but the author uses the image of a vulture, known for its scavenging nature, to describe the jeweler's greedy and opportunistic behavior.
The sentence implies that the jeweler is being overly attentive and perhaps even predatory in his examination of the diamond, just as a vulture would be when inspecting a carcass.