The gate is on the other side. No, the other side. The other side, horse! The gate is on the other side. If you’ve ever seen your horse get "stuck" in a pasture because they’ve "forgotten" where the gate is, you’re likely not alone. And when it comes to spatial cognition, the old adage “stubborn as a mule” might better be said, “stubborn as a horse” or "sensible as a mule."

According to recent research by British scientists, mules appear to have a faster capacity to learn about spatial relations—figuring out where things are, or navigating around objects—than horses and donkeys.

And when objects get moved and the animals must find new paths around them, horses stand out as being particularly attached to their old ways. In other words, they tend to stubbornly insist that the old way is still the right way. Yep, stubborn as a mule. Or horse.

“I would say that mules in general are smarter than horses and donkeys, based on our findings so far,” said Britta Osthaus, PhD, researcher in the psychology department of Christ Church University in Canterbury, UK. This could be attributable to what she calls “hybrid vigor”—or “the advantageous combination of parental traits,” Osthaus said. “In the mule this would mean they are better in the cognitive tasks we have set them to so far.”

These cognitive tasks started with a simple design of setting up a fence between the animal and its food, with an open gate at one end of the fence. The researchers tested 12 horses, 12 donkeys, and 12 mules as they each tried t