back zerbert
Similar to the normal zerbert, this is when one individual uses his or her mouth to create a seal with another individual's back and then blowing, producing a fart-like sound. The back zerbet is often more tricky to pull off given the higher concentration of muscles compared to the stomach and so it is best pulled off by an experienced zerbet giver.
I was watching Lynn and Nicholas wrestle when she decided to hold him down, face first, and give him a legendary back zerbert. The noise was so loud; she has clearly done this before.