talk the hind legs off....

[crisgal]

....a donkey.
Why do we say it?

[rd14962]

It is meant as an expression that the person doing all the chat, could convince a donkey (a stubborn animal at the best of times) to sit down on it's haunches, something it just wouldn't do.

[Quizmonster]

The phrase �talking the hind leg off a �horse' was first recorded in 1808. Only later did people convert it to a �donkey' and even a �dog' was used as the poor suffering creature, too! The quote it appeared in back then referred to the saying as an "old vulgar hyperbole" (common exaggeration). Obviously, therefore, it had been around for quite some time prior to that.
I'd guess that it was based on the fact that a horse has rather long legs and anyone who can talk the hind leg off such a creature is obviously one who can go on speaking for a long time.
In other words, it may well be similar to the way we use 'donkey's years' to mean a long time, based on the original form of the saying which was 'donkey's ears'...ie something else very long, too.
Alternatively, perhaps the idea is that people who do talk incessantly - not caring whether they are talking to a human being or an animal - would even bore the poor creature to such an extent that it would be forced to sit down exhausted in the end...ie it no longer needs its hind legs, as suggested in the answer above.

[crisgal]

hi QM, I wondered if you'd stop by! :)

Very interesting, thank you x

[Quizmonster]

Always a pleasure, ma'am!