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."
The perception of geese as being particularly stupid and emblematic of foolishness has four possible sources. One source is their ungainly, waddling walk, which makes them look clumsy when on land, despite their grace in the water. The second source is that the goose was the emblem for a vain or silly man in ancient Egyptian hieroglyphics. The third source is that the goose is often portrayed as being the unwise or gullible one in fairy tales and fables, such as “The Fox and the Goose”. The fourth source comes from the fact that male geese often overreact to perceived competition from other males. If their mates come too close to another male, the angry goose will stand in between them, comically waggling its wings and making hissing sounds to deter his rival.