Help! "Sometimes I think evil is a tangible thing- with wavelengths, such as sound and light have."

Is this quote a simile, metaphor, or personification? With that, what effect does it create?
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Read this excerpt from the grapes of wrath: snub-nosed monsters, raising the dust and sticking theirsnouts into it, straight down the country, across thecountry through fences, through dooryards, and in and outof gullies in straight lineswhich best describes the tone in this passage