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.
(..) you know. How do you know it's love if you've never been in love before? 'Cause I feel it. Where? In my stomach. It's all warm. I always had a knot there, and now it's gone. Mathilda, I'm glad you don't have a stomachache anymore. (..)1994 Léon: The Professional
(..) You're going too far right now. I'm gonna be late for work. How about working at home today? Really feel it. That's it, stomach in. - One- - Now it's my turn! Shit! She's gonna hit me! - Daddy, she's- (..)1994 Léon: The Professional