Posthumous Equine Abuse

This'll just be a quickie, before I forget.  I just used the phrase "beating a dead horse" in a work email, without really thinking about it.  Then, after sending, I realized that I was sending it to a group of Chinese colleagues.  This is the type of stuff you don't really have to think twice about when dealing with native English speakers, but I think I may have to be more careful going forward.  Because if they don't grasp the idiom, they may be worried that their new goofy-looking American colleague is far far more deviant than his big red head suggests....