When Waverly's mother specifies that her soup at the restaurant must be served very hot, Waverly says that "it was by her tongue's expert estimate 'not even lukewarm.'" Of course, one's tongue is not actually capable of being an expert or making an estimate, but the tongue works together with one's brain to respond to heat or cold; the whole self is needed to perform this action. Therefore, Waverly uses synecdoche—when one substitutes a part for the whole—to describe her mother's response. It makes Waverly sound rather wry and ironic, as though she is mocking her mother a bit.
Waverly also uses a metaphor—a comparison of two unalike things where one is said to be another—when she describes a telephone that her daughter and her fiancé took apart as "disemboweled." A phone does not actually have bowels, but people do, and this comparison helps to establish the mood of the chapter, as Waverly is feeling uncertain and fearful of her mother's response to her news. This is also an example of personification, or ascribing humanlike qualities in inhuman things.