1. You will never be hired as an exterminator.
  2. You may grow attached and not want to get rid of him. Now you have a pet mouse to take care of.
  3. He's only going to take like 4 bites and then say he's "full".
  4. You will have one less cookie and that is equal to hell.
  5. He's going to tell all of his mouse friends that you're just giving it away for free. You will be liked but not respected by the mouse community.
  6. He still won't love you.
    Suggested by @daniel