Brain Teaser

I heard a schoolkid say the phrase mental brain today. The word mental was being used an adjective.

I had to think about this. Can the brain be described as mental? Is it like saying a thoughtful brain or a mindful brain? Are these rubbish?

I suppose they could be tautologies. Where you say the same thing twice without one of the words being needed. Like hot fire or wet rain or living animate objects or missing one out alternately.

Can you think of better examples? What about the toy shop was full of toys?