The incident referred to in the question occurred on July 22, 1943 while a U.S. armored column was under attack from German aircraft, he shot and killed a pair of mules that had stopped while pulling a cart across a bridge. The cart was blocking the way of the column. When their Sicilian owner protested, Patton attacked him with a walking stick and had his troops push the two mule carcasses off the bridge. Axelrod, Alan (2006), Patton: A Biography, London: Palgrave Macmillan, ISBN 978-1-4039-7139-5, pp. 105–07.
When the movie “Patton” was first released, the most controversial scene in this film was not the slapping scene but that in which General Patton shoots a pair of mules that are blocking a bridge and dumps their carcasses over the side. While the true fate of the two animals is still unknown. The fact is that no actual animal cruelty appears onscreen. Rather, in distinct cuts, Patton draws his revolver, gunshots are heard, two dead mules are seen in the roadway, followed by a wide, distant shot of the carcasses as they are tossed from the bridge. Therefore, actual shooting or cruelty was only inferred by the audience. The Society for the Prevention of Cruelty to Animals protested the scene loudly in the press, but they did so with absolutely no evidence of animal cruelty in this scene.