It must be practiced. If he holds a flower, laugh. If he just sits silently facing a wall, cut off a body part and throw it at him. To find the answer, drop the question. Beware, the kyosaku stick.
Zen koans are unanswerable questions given to students to frustrate their rational minds.
After long periods of searching for the answer the student will not only drop the search, but will drop the question. Zen is a dropping or emptying of the mind. After a time, the search for the answer disappears, the question disappears, the ego disappears, and what is in that moment is. It is different from other forms of meditation in that it does not require the student to hold or concentrate on any one object. As usual, just the opposite.