An inquisitive young man was travelling in the train to another region in his country.He noticed that the old man in front of him kept tilting a bottle he had in paper bag and taking a drink.He got more and more mystifyed as he saw that the man did this every 5 minutes or so.A burning desire grew in him to check the bottle and its contents.When the old man finally got up to use the restroom the young man siezed the opportunity and drank off the bottle.He tasted something sticky and tasetless.Upon the return of the old man the young man said to him"Sir, forgive me ,because I took a drink from your bottle to taste the drink you seemed to like so much,but i tasted something I have never tasted before.Can you tell me what it was. The old man smiled at the youmng man and said"you dumbass ,that was no drink.I have tubercolosis and that was my saliva that I spat into the bottle"