The riddle hinges on the phrasing and the nature of the word 'pick up.' The question asks why zero toy fishes were picked up, and the answer is that you don't 'pick up' fish—you catch them. The materials of the toy fishes (iron, wood, and copper) are a red herring. The riddle plays on the assumption that the method of collection is about picking up, when in reality, the action is about catching. This wordplay is the core of the riddle, not the magnetism or the materials of the toy fishes. The initial explanation that the toy fishes were stuck to a magnet is flawed because it doesn't address why none were picked up. The correct interpretation is that the word 'pick up' is misleading, and the answer is simply that you catch fish, not pick them up.