How to find out if two people are mutual friends?

[Lucas C]

If two of the people hid their friend's list from everyone else(they are both my friends) on facebook, Is there any other way you could find out if they are mutual friends? If you know what I mean, usually when two of the people hide their friend's list, you can't see if they are mutual friends or not. So does anybody know is there is another way? 10 points for best answer!