Now I know that "brains" plural is only used for intelligence. But both "brains" and "brain" can be used for an organ in the head.

So, how do you tell when you will use singular or plural brain for physical organ?

Can you give me some examples?

I know one context that plural will be used is when brains are shot by a gun
"I'll blow your brains out."
But what about singular?
"A brain of this cat is larger than normal."?

Question

Now I know that "brains" plural is only used for intelligence. But both "brains" and "brain" can be used for an organ in the head.

So, how do you tell when you will use singular or plural brain for physical organ?

Can you give me some examples?

I know one context that plural will be used is when brains are shot by a gun
"I'll blow your brains out."
But what about singular?
"A brain of this cat is larger than normal."?

Answer

It’s anatomically and grammatically incorrect to use the plural form to refer to the brain of one person.

You will only hear “brains” referring to one person in slang and colloquial phrases such as the ones you’ve mentioned.