Why Do We Say "silly Goose"?
The expression “silly goose” refers to a person who acts in a childish, foolish but somewhat comical way. This term originates from several sources. The entry in the Brewer's Dictionary of Phrase and Fable states, “A foolish or ignorant person is called a goose because of the alleged stupidity of this bird." The Samuel Johnson dictionary describes geese as, “Large waterfowl proverbially noted, I know not why, for foolishness."