脑洞大开(nao dong da kai)


"脑洞" (nao dong) is derived from "脑补" (nao bu). "脑洞大开" (nao dong da kai) means "脑补" (nao bu). Usually it refers to supplementing some plots to the brain and fancying some plots that do not happen in comics, fiction and reality in the mind.

"脑补" (nao bu) also means mental masturbation and exerting unlimited imagination.