What's eating (someone)?
What's bothering someone? Why is someone in a bad mood? What's eating Terry today? I asked him how his weekend was and he just glared at me. I've never seen her act that way before. What's eating her?
What's eating someone?
Inf. Fig. What is bothering someone? Tom: Go away! Bob: Gee, Tom, what's eating you? Bill: Tom's so grouchy lately. What's eating him? Bob: Beats me!