RichThesaurus
have bats in one's belfry
vs
have squirrels in one's attic
have bats in one's belfry
verb
To be crazy or eccentric.
have squirrels in one's attic
How often have the words
have bats in one's belfry
and
have squirrels in one's attic
occurred in a corpus of books?
(source:
Google Ngram Viewer
)