Something fun I read when finding a link for this story:
He was the one that started the long-standing rumor/legend that they made Mr Ed "talk" on the show by putting peanut butter in his mouth. The studio had asked him not to reveal the method to make the horse move his lips, but he kept getting asked the question. So he just made up the idea about peanut butter so that people would stop asking.
Apparently eventually he revealed that they tried to do it mechanically (like with wires or something) and eventually just found that the horse's trainer was able to teach him to move his lips by touching his hoof while out of the view of the camera, and even to hit his "cue" by noticing when Alan Young would stop talking and starting to move his lips then. That's one damn smart horse.