I hear young children calling people a silly goose when they do something that the kids think doesn't make sense. What is the origination of the phrase?
So I think there is a sub for word origins and I hope I'm not violating the rules by answering you.
Silly originally meant "pious" and was applied to the animals both sheep and goose. Goose was meant to imply happy/innocent and sheep innocent/pure.
I'm not sure when it came to be used as it is now, but the affectionate term had a different use once. Again another sub could probably tell you more.
Source: The Lost Language Of Symbolism by Harold Bayley