Twenty-three horses in Norway were tutored to recognize symbols corresponding to blanket preferences. A dark horizontal bar on a white board meant, "Yes, I would like a blanket." A blank board meant, "I'm fine as I am now." And a vertical bar on a white board meant, "Please remove my blanket."
Researchers found that, after a few minutes of training per day, all 23 horses learned what the symbols meant in just two weeks. By the end, all the horses could touch the symbol with their muzzles to tell the people what they wanted.