The "Horse Whisperer" and a question about that

OH Wilburrrrrrrrrrrrrr!

I think what you mean about a parallel is that they both involve horses. However "The Horse Whisperer" refers to a man who can communicate (to a degree) with horses. The expression "straight from the horse's mouth" might have originated in reference to "looking a gift horse in the mouth" (or any horse really) to see its teeth to see how old it is. It would be akin to examining any potential gift with a critical eye as to its worth rather than just graciously accepting it. However the expression about something being "straight from the horse's mouth" refers to getting information straight from the source of such information, as in examining the horse's teeth to see how old it is.

Hope that helps...

I thought the original post was meant as a joke about horses being able to whisper.
Horse Whisperer = Whispering Horse?

AFAIK 'straight from the horse's mouth' was an expression used by racing tipsters to imply that the information they were trying to sell came from inside sources - since no-one would know more about the condition and willingness to run of a particular horse than the horse itself! 'Straight from the stable cat' was a similar expression.

The expression could have indeed come from the touts at the tracks, in which case it was probably less reliable than actually looking in the horse's mouth...