Do You Have “Extra” Keys on Your Key Ring?

Last night a coworker of mine lost his keys.  He called me because he he needed a new key to the office.

I carry a spare so I grabbed my key ring and started to search for the extra.  That's when i noticed something odd.  I have TWO keys on my keyring and I have no idea what they go to.  I have gone through every possible door, file cabinet and mailbox and all my keys are accounted for.

What the heck?!  How do you end up with keys and have no idea what they're for?  Do you have any keys on your ring that you don't know what they go to?