Jimmy Stewart (about Pie): “The horse was amazing. I rode him for 22 years. I never was able to buy him because he was owned by a little girl by the name of Stevie Myers, who is the daughter of an old wrangler who used to wrangle horses for Tom Mix and W.S. Hart. He retired and he gave this horse to her. He was a sort of a maverick. He hurt a couple of people. I saw him when I started making Westerns. Audie Murphy rode him a couple of times. He nearly killed Glen Ford, ran right into a tree… But I liked this darned little horse. He was a little bit small, a little quarter horse and Arabian. I got to know him like a friend. I actually believed that he understood about making pictures. I ran at a full gallop, straight towards the camera, pulled him up and then did a lot of dialogue and he stood absolutely still. He never moved. He knew when the camera would start rolling and when they did the slates. He knew that because his ears came up.”
From a great BFI interview from 1972. You can read the whole thing here. Photo of Stewart on Pie from The Far Country (1954).