Riddle: One day a man walked onto a train and sat across from a woman. The woman took off her glove and he killed her.
Answer: When the man saw the woman he actually did not recognize her at all even though they had previously been married. When she took off her glove he saw that she only had one finger. The missing finger brought back memories of when she had framed him by cutting off her own finger, leaving traces of blood around the house and framed him for murder. When the man saw her he remembered that you cannot be charged for the same crime twice and therefore used the law of Double Jeopardy against her.