Best Human

A sage presented a prince with a set of three small dolls. The prince was not amused.
"Am I a girl that you give me dolls?" he asked.
"This is a gift for a future king," said the man. "If you look carefully, you'll see a hole in the ear of each doll."
"So?"
The sage handed him a piece of string.
"Pass it through each doll," he said.
Intrigued, the prince picked up the first doll and put the string into the ear.
It came out from the other ear.
"This is one type of person," said the man. "Whatever you tell him, comes out from the other ear. He doesn't retain anything."
The prince put the string into the second doll. It came out from the mouth.
"This is the second type of person," said the man. "Whatever you tell him, he tells everybody else."
The prince picked up the third doll and repeated the process. The string did not reappear from anywhere else.
"This is the third type of person," said the man. "Whatever you tell him is locked up within him. It never comes out."
"What is the best type of person?" asked the prince.
The man handed him a fourth doll, in answer.
When the prince put the string into the doll, it came out from the other ear.
"Do it again," said the sage. The prince repeated the process. This time the string came out from the mouth. When he put the string in a third time, it did not come out at all.
"This is the best type of person," said the sage. "To be trustworthy, a man must know when not to listen, when to remain silent and when to speak out."