I was reading up on my diabetes notes and there's an actual brand-name drug named "Mixtard".
Tell me you don't read that and think of a retarded centaur and I'll give you a dollar. All I can picture is a horse with a human torso who just happens to have Down's syndrome trying to walk and yeah...
But realistically, if centaurs exist - as in humans with horse bodies - there's bound to be a mentally challenged one here and there, and as intelligent/caring creatures, they aren't going to make like lions and eat their retarded babies. So, eventually, there will be a fully grown mentally retarded centaur.
I believe one of those centaurs was diabetic, and the other centaurs figured out a drug to save him, and we humans discovered it from them. So, of course, we called it Mixtard, as a homage to the true genius who discovered it - the centaurs.
Or maybe we homo sapiens are just a bunch of fucking idiots.