Take this medication 'on an empty stomach'. [=when your stomach is empty because you have not eaten for a time]
When I had the flu, just the thought of eating made me 'sick to my stomach'. [='nauseous']
She felt a flutter in 'the pit of her stomach' when he walked through the door.
(..) -I'll see you tonight? -Okay. In my hotel, there's always somebody watching . I'll see you tonight. Weak stomach, Mr. Zerga? I don't believe in weakness. It costs too much. I don't believe in questions either. Oh, really? Well then, let me give you a tip. (..)2001 Ocean's Eleven