A simile uses the words "like" and "as" to compare two often unconnected items. There are quite a few examples of similes in the novel:
He was tall and bent and his thin beard straggled up his cheeks like dry moss on gray rocks. His eyes were dark and expressionless, and set so deep under heavy brows that from a distance they looked like dark empty holes.
Here, the author uses similes to describe the children's initial feelings of apprehension about the professor. He is a figure of mystery to them, and they hardly know what to make of him. Essentially, the professor's reclusive habits fascinate the children, and they engage in speculations about his true character.
They didn’t say a word, but with widening eyes and small taut smiles they sent a charge of excitement dancing between them like a crackle of electricity.
Here, the children discover what they later call "Egypt." This location is actually the storage yard behind the professor's store. When the children enter the yard, they see a broken birdbath, a statue of Diana the Huntress, a stack of wooden porch pillars, and a bust of Nefertiti. April, Melanie, and Marshall are thrilled at their discovery. The author tells us that a "charge of excitement" passes between April and Melanie, and it is like "a crackle of electricity." Throughout the novel, similes like the ones above reinforce the importance of fantasy play in the children's lives. For someone like April, it is one way to navigate feelings of abandonment and loneliness after her mother goes on tour.