I wonder where that phrase comes from. It's not like people beat up living horses, so why beat up dead ones?
"TheEngineer" wrote:
First, from www.phrases.org.uk:
flog (or beat) a dead horse. Though he supported the measure, British politician and orator John Bright thought the Reform Bill of 1867, which called for more democratic representation, would never be passed by Parliament. Trying to rouse Parliament from its apathy on the issue, he said in a speech, would be like trying to 'flog a dead horse' to make it pull a load. This is the first recorded use of the expression, which is still common for 'trying to revive interest in an apparently hopeless issue.' Bright's silver tongue is also responsible for 'England is the mother of Parliament,' and 'Force is not a remedy,' among other memorable quotations. He was wrong about the Reform Bill of 1867, however. Parliament 'carried' it, as the British say." From the "Encyclopedia of Word and Phrase Origins" by Robert Hendrickson (Facts on File, New York, 1997.)
UsingEnglish.com defines "beating a dead horse" the same way, with an actual dead horse.