“between” vs “among”
I learned that "between" refers to two objects or concepts and "among" refers to three or more. However, in situations when I am asking about distinctions, it seems correct to say, for example, "What is the difference between a horse, a zebra, and a mule?" as opposed to saying, "What is the difference among a horse, a zebra, and a mule?"
What is the rule for questions like this about the "differences between" several things?