For example, lions and tigers, or polar and grizzly bears, are not the same animals, but, they have the same sequence of base pairs, so they can mate. Even if they find a way to mate, cats and dogs still can’t produce their hybrid.
Dogs do all kinds of weird stuff. They can mount and hump anybody or anything, due to variety of reasons, such as excitement, boredom, stress, anxiety, etc. Also, a dog might be humping a cat to show his dominance.