A bank was robbed by an armed robber.
  He walked into the bank, went up to the bank teller, pointed
a gun at her and said, “Give me all the money or I’ll shoot.”
  The bank teller was frightened and did as the robber
asked.
The police later asked the bank teller if she could tell them
anything about the robber.
  “He wore a stocking over his face,” the bank teller said. “I’m
afraid I can’t tell you what he looked like.”
  A week later, the bank was robbed again.

  “I’m sure it was the same man,” the bank teller said. “I

didn’t see his face because he had a stocking over it again, but
the voice was the same when he said, ‘Give me all the money
or I’ll shoot.’”
  A week later, the bank was robbed for the third time.
  “Was it the same man?” the police asked the bank teller.
  “Oh, yes, I’m sure it was,” the bank teller said. “I didn’t see
his face because he wore a stocking over it again, but it was the
same voice.”
  “Are you sure you didn’t notice anything else about the
man?” the police asked. “A little detail will do. Tell us anything
that might help us find him.”
  The bank teller thought for a minute, then she said, “There
is one thing.”
  “And what is that?” the police said hopefully.
  “Every time he comes in and robs us,” the teller said, “he’s
better dressed than before.”

          银行劫匪
  一家银行遭到持枪歹徒的抢劫。
  他走进银行，径直走向银行出纳员，用枪指着她说：“把所有的钱都交
出来，否则我毙了你。”
  银行出纳员吓坏了，遵照劫匪的要求做了。
  后来警察问出纳员是否能描述出劫匪的特征。
  出纳员说：“他脸上蒙着丝袜，恐怕我无法描述他的面部特征。”
  一周之后，这家银行又遭抢劫了。
  出纳员说：“我确信是同一个人。可我没看清他的脸，因为他这一次还
是蒙着丝袜。但是，当他说‘把所有的钱都交出来，否则我毙了你’的时
候，我能听出是同一个人的声音。”
  又过了一周，银行又遭抢劫了。
  警察问出纳员：“是同一个人做的吗？”
  出纳员说：“哦，是的，我确信是同一个人。我没看清他的脸，因为他
仍然蒙着丝袜，但听声音是同一个人。”
  警察问：“你确定没有注意到任何其他有关这人的细节吗？哪怕一点蛛
丝马迹？任何事情都可能对我们的破案有帮助。”
  出纳员想了一会儿，说：“哦，有一件事。”
  “什么事？”警察满怀希望地问。
  出纳员说：“每次他来抢劫，都比前一次穿得更好了。”