flog a dead horse

• beat a dead horse
• flog a dead pony

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flog a dead horse

1. (dated, nautical) To attempt to get extra work out of a ship's crew during the dead horse period.
2. (Britain, idiomatic) To attempt to get more out of something that cannot give more; to attempt to arouse fresh interest in something that is either hopeless or already settled.

• spit in the wind

• necrohippoflagellation
• necrohipposadism