APAD: What's eating you?

Definition

   question to a person who seems emotionally or mentally consumed by some    

   internal distress

                                                                              

Examples                        

   1) What's eating you? You seem really upset today.                         

   2) I can tell something is bothering you. What's eating you?               

 

Etymology

   It is likely from the idea of parasites eating away at food.               

 

Synonyms

   What's bothering you?, What's got you down?

 

- englishdaily626.com [edited]

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Maybe it was to answer that question, Dorothy Parker wrote

   The sun's gone dim, and

   The moon's turned black;

   For I loved him, and

   He didn't love back.