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.
(..) It was either this or a Huey from Vietnam. I figured a boat would be more practical. What's going on? Pretty much exactly what you think goes on inside of a stomach. You're right. That really is the worst way to die. Reardon! What in Hades is going on with my engine? Is it ready yet? (..)2013 Percy Jackson: Sea of Monsters
(..) It's not working! The Sea of Monsters might not be in Poseidon's domain. Hold on! Where are we? Smells like the stomach. Watch your step. What is this stuff? I don't think you want to know. This has to be the worst way to die, ever. Yeah, everything that disappears (..)2013 Percy Jackson: Sea of Monsters