Maybe a hint will help? A new verb is needed. Read this carefully. Duck are natural hunters.
Try droping on ground something that lives in water. Corn is just too big. Caterpillars or other possible food is a scenery type object because the game allows to create it again and again after eating it. But you only can have each object one time in inventory. It is set so for the hunger system. So use that new verb to obtain an actual item object that you can eat or use somewhere else.