The teacher stood with his back to the (11) on a winter morning. He decided to give good (12) to the pupils before starting

The teacher stood with his back to the fireplace on a winter morning. He decided to give good advice to the pupils before starting the lesson.
   "Before you speak, think. Count 50 before you say anything important, 100, if it is very important."
   The lips of his pupils were moving in unison, and suddenly they burst out in chorus: "99,100. Your coat tails are on fire, Sir."