I have read a story called 'The restaurant at the end of the universe'. I have difficulty in understanding 2 sentences:

'Arthur stared at his feeling slightly ill.'

I think it means that the person Arthur looked at was feeling ill, and not Arthur himself...is that right?

"Hey, Earthman, - said Zaphod with a malicious smile on the face that wasn’t stuffing itself – what’s eating you?"

I know the expression 'to stuff oneself', but what does it mean here? It means that he was eating a lot and quickly?

'What's eating you?' - What is bothering you? Why are you upset?

Thank you for your help!
Kind regards.
The preceding sentence refers to the waiter bringing over steaks. The sentence that follows: "Arthur stared at his (steak) feeling slightly ill."

What's eating you? Means "What is on your mind or what are you worrying or thinking about?"

"on the face that wasn’t stuffing itself" refers to the fact that Zaphod actually has two heads and thus two faces. One of them was stuffing itself (meaning eating a lot and quickly), while the other face/mouth asked the question.
You need to post the context with a troublesome sentence:

A matter of minutes later the waiter arrived with four huge steaming steaks. Zaphod and Ford wolfed straight into them without a second's hesitation. Trillian paused, then shrugged and started into hers.
Arthur stared at his feeling slightly ill.
Hey, Earthman, said Zaphod with a malicious grin on the face that wasn't stuffing itself, "what's eating you?"

The waiter brought four plates, one for Zaphod, one for Ford, one for Trillian and the last for Arthur.
Three of them started eating. Arthur just looked at his steak, He felt ill. He didn't eat.

Your interpretation of "stuffing oneself" and "What's eating you?" is correct.
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Thank you veru much for all the helpful posts!
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