Spot the error: Answer

Well, Nikhil had to get it right. After all it has to do with the history of photography and for all his maniacal insistence on knowing the ins and outs of the trade, it's only expected.

The above image is one of the many in which horses were shown galloping with their legs splayed apart. Somehow, such an image appeals to our sense of speed and agility that we associate with horses so art accordingly imitated our prejudices. It wasn't until the late 19th century that a person named Eadweard Muybridge studied the motion of horses by taking a series of photographs and running them consecutively at a high frame rate to produce an illusion of continuous reality. Here is what he saw:

As you can see, he demonstrated that the legs of a horse, when in air, are never splayed apart. This, incidentally, is the first motion picture ever produced. So there you are.