A biology teacher wished to demonstrate to his students the harmful effects of alcohol on living organisms. For his experiment, he showed them a beaker with pond water in which there was a thriving civilization of worms. When he added some alcohol into the beaker the worms doubled-up and died.
"Now," he said, "what do you learn from this?"
An eager student gave his answer.
"Well the answer is obvious," he said "if you drink alcohol, you'll never have worms."