Kelpie

What are the chances of a contestant coming up with the words "water spirit", let alone "shape shifting"?

Granted, this is how kelpies are defined on Wikipedia; but you can't always expect contestants to express themselves in exactly the same words as Wikipedia. In other words, you can't rely on Wikipedia to write your answers for you.

To my mind, it would be far better if the question setter had omitted the word "horse-head". This would have left the door open to answers such as "supernatural beings in the shape of a horse" - but the answer would still have needed to make allowance for a variety of different forms of words.

Even better, the question could have described the sculptures and the water-spirits that they depict, and ask what they were called.