beat a dead horse

• flog a dead horse

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beat a dead horse (third-person singular simple present beats a dead horse, present participle beating a dead horse, simple past beat a dead horse, past participle beaten a dead horse or (colloquial) beat a dead horse)

1. (idiomatic) To persist or continue far beyond any purpose, interest or reason.

   After having shown us three hours of instructional and safety videos, the inspector was simply beating a dead horse by telling us to buckle up as we got into the van.

• necrohippoflagellation
• necrohipposadism