Have nothing between the/(one's) ears phrase
Used to imply that someone is very stupid
He doesn't have a lot between his ears.
She couldn’t become such an exceptional doctor if she had nothing between the ears.
Only those who do not have much between the ears believe that story.
To have no money
Used to describe someone who is naive, gullible, inexperienced, easily fooled, ignorant, unsophisticated, etc.
To say, or believe something or someone that seems completely crazy, delusional, or stupid
A person who is low-witted or stupid
To be extremely stupid; not to be alert
The verb "have" should be conjugated according to its tense.
The idea of the idiom comes from the fact that “between the ears” is where the brain is. So, if you say someone has nothing between the ears, you mean they are stupid or have no brain.