When a lion became old and haggard and was unable to hunt, he realised that he would have to resort to more cunning and less to physical power. So he declared himself sick and retired to his den. Whenever anyone of his subjects came to pay a visit to him, he would grab and eat it up.
Then, one day, a fox came. But before entering the den she very carefully looked around and decided to remain at the entrance only.
“Please come in, dear fox,” said the lion in a very mild tone.
“Thank you very much!” the fox said. “I would rather prefer to remain only at the entrance.”
“No formalities please, do come in,” the lion said in a sweet voice.
“Thank you, very much,” said the fox. “I can see so many footprints going in, but not one which comes out.” And she went away.
The lion had to remain hungry that day.

Moral : It pays to be vigilant.