Like a burp, but with a hint of puke.
"When I saw the monkey pee in it's mouth, it made me wanna blarch."
Blarch was an exclamation originally used in Ancient China, in the provinces near present-day Shanghai. It was used most often when one burned one's tongue and distorted natural pronounciation habits.
Lao Gao took a sip of the soup and unexpectedly screamed "blarch!"