...una cabeza fría...
From the context I'm thinking closed minded e.g. "a mind like a steel trap.
The scene is towards the end of this clip: Tiempo Final
3 Answers
Closed-minded and a mind like a steel trap do not mean the same thing.
Closed-minded means that you are not open to argument or persuasion, stubborn, bull-headed. A mind like a steel trap means that you are very perceptive, astute, nothing gets past ;you.
According to this discussion tener una cabeza fría means that you are level-headed.
Now I'm thinking it almost traslates literally to a cool head, which gives me an idea for the phrasebook:
Las cabezas mas frías irán ganar.
Roughly: Cooler heads will prevail.
to be able to think very quickly, clearly and intelligently She'll be a brilliant lawyer - she has a mind like a steel trap.