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.
(..) What is this? It was a slow week. I mean, that's half of what I got. You hear this, Louie? I'm starving here. And when the old stomach starts talking, it's not talking to me. - It's talking to... the claws! - Not the claws! Please! I'm holding these bad boys back as best as I can, but the thing is it's not up to me. The stomach got a direct line to these babies,... ...and I'm picking up a lot of chatter! So, I'll talk to the claws, but in exchange... ...next week, all your food comes to me. (..)2008 Bolt