RichThesaurus
slow on the uptake
vs
two sandwiches short of a picnic
slow on the uptake
adj
Of a person, slow to comprehend or process intellectually.
two sandwiches short of a picnic
How often have the words
slow on the uptake
and
two sandwiches short of a picnic
occurred in a corpus of books?
(source:
Google Ngram Viewer
)