I am reminded of my first encounter with mules, two mule trains on a Sierra Club High-Light trip back in 1971. Each train was led by a horse (animal racism: the mules would always follow a horse under the assumption that it was a superior being).
On one of the early evenings on the trip, we stopped at the mouth of a canyon to set up camp, and the mules were all untied and set free. The horse leaders began wandering up the canyon, grazing as they went. For a few minutes the mules lined up behind the horse in their usual order, following meekly along. Suddenly one and then another realized that they weren't tied together any more and kicked up its heels and trotted off in a different direction, clearly delighted at the sense of freedom. It took several minutes before all of the mules made the same realization.
They didn't go far, and the crew found it easy to round them up again fro work the next morning.
But I never saw them line up side-by-side, in either order.