An idiom meaning people of the same stripe—especially two or more who are similarly bad or culpable; similar to 'birds of a feather' or 'two of a kind' (usually negative).
あの政治家と企業の幹部は同じ穴のムジナだと言われている。
People say that that politician and the company executive are two of a kind.
表向きは対立しているが、実際は同じ穴のムジナだった。
Although they seemed to be opposed on the surface, in reality they were of the same stripe.
あの二人は口では正義を語るが、やっていることは同じ穴のムジナだ。
Those two talk about justice, but what they do makes them two of a kind.