@
cbeckerson
The saying comes from the old days when horses were in common use. You can check the age and condition of a horse by looking in their mouth. If someone were to give you a horse (a very valuable thing in those days), you would not open the horses mouth to check the age or condition, you would just be thankful for the gift.
Even today the first thing most vets will do is to look in the horse's mouth when they meet a new horse they have not worked on before.
Lets just hope we don't see Barry looking in the mouth of the milesplit rankings guys!