When someone says you are "talking to a dead horse," they mean that you are wasting your time trying to convince someone of something or discussing a topic that has already been settled or is unlikely to change. It's an idiom that suggests futility in continuing the conversation, as the issue is effectively "dead" and cannot be revived. Essentially, it's a way of saying that further discussion is pointless.
It means that you should stop talking about the subject because it's useless and already been talked about enough. (A dead horse won't do anything for you, no matter how many times you beat it.)
"When the horse is dead, get off" means you should not waste time on things that are not worth it. If the horse is dead, you can't ride it any more.
It means that the male horse cannot reproduce.
They have an interest in you or in talking
If a horse whickers, whinnies or neighs it is usually because something has his/her attention, like another horse in the area or it can be a warning to you of something odd the horse is not sure of.
It means that someone is renting a horse for use.
The actual quote is "stop beating a dead horse" stop wasteing time on a pointless activity.
This is supposed to mean that someone is talking about you.
They are dead
to stop talking
If someone says "it's been a pleasure talking to you," they mean "it was nice talking to you and I enjoyed it."
I think this may be more of a literary question than a horse one... I believe it refers to "flogging a dead horse" which it a way of saying you are trying to get get results when the issue has been resolved or dropped.