Are you sure it's very much out of his stomach? I believe what you're referring to is a common expression we have in English: to have butterflies in one's stomach. It means that someone's nervous :) You know, when you're nervous, you have this fuzzy, uncomfortable feeling in your stomach? That's what they're describing.

The idiom (and it's a common one) is "have butterflies in my stomach." It is a common description of "stage fright," the feeling that many people get before they need to perform in front of an audience. Situations that cause it include: an actor about to step out on stage; a person about to give a speech in public; a musician about to play a solo in front of an audience. It suggests mild nausea--gentle butterflies are lightly tickling you from inside. It's a bad feeling. It is surprisingly common even among successful, experienced actors, speakers, and musicians who have been performing for decades. This is a joke that's no an idiom, but in a course on public speaking they said "You can't always get rid of butterflies in your stomach, but you can make them fly in formation." The idea was that you could feel the fear but perform anyway.