After you've eaten a hearty meal, and quite possibly drank a good amount of your liquid of choice, you may have burp-soup. This is when you burp, but instead of just air you get a little something extra that comes up with it. It's not enough to qualify as throwing up, because it's an amount which is generally small enough to simply swallow again while making a disgusted face.
*buuuurrrrrrppp....swallow* "oh man you guys, I just had the sickest case of burp soup!!"
Your friend brings up what sounds to be an especially juicy belch, you then reply, "niiiice, little burp soup there?"