頭を冷やせ。

head; hair (on one's head); mind; brains; intellect; leader; chief; boss; captain; top; tip; beginning; start; head; person; top structural component of a kanji

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to cool (from room temperature); to chill; to refrigerate; to calm down; to cool off; to regain one's composure; to relax; to be frightened (at); to be scared (of)