The theory, well my theory is that some creatures are the result of oddly combined other things.
The majestic unicorn
It is the result of a horse and a rhino falling in love.
|Is it a bear? Is it a dog?|
It is the love child of a dog and a teddy bear.
|dog humps teddy bear|
|The cutest animal in the world in my opinion|
It is the result of an alien invasion.
|ET loves ostrich|
It is the result of some kind of aquatic life bestiality.