For those who don't read The Right Way by Jennifer Stewart, a fun/pun from her recent effort:
There was once a very smart horse. Anything it was shown, it mastered easily, until one day, its teachers tried to teach it about rectangular coordinates, and it couldn't understand them.

All the horse's acquaintances and friends tried to figure out what was the matter and couldn't. Then a new fellow looked at the problem and said, "Of course he can't do it. Why, you're putting Descartes before the horse!"
Grrroooooan !
(The louder they groan, the better they like it!)

But that horse would have eaten up Pascal.(celery)

pascal celery
Noun 1. pascal celery - any of several types of commercially grown celery having green stalks
Paschal celery
celery - stalks eaten raw or cooked or used as seasoning

I detest green celery which has a bitter tasted. When I was young, the celery sold then had blanched stalks, because soil had been banked up around it, so light could not reach it and promote growth of chlorophyll, which causes the bitter taste. Also it came with the roots on it, and they were the best tasting part of the whole stalk. Except the bunches were held together with long slim nails. The nail holes had to be cut out, because the farmers held the nails in their mouths. Yuk.

For a rather long classic psychology story about a clever horse, read about Clever Hans at:
http://www.thoemmes.com/psych/pfungst.htm