[casouniquo]

There are certain conditions to be met.

A - Friends Hidden. B - Friends Hidden. A and B are Friends. C - Not friends with A and B.

if C views mutual between A and B, C sees only the list of mutual friends between A and B whose friends lists are open.

i.e. if the list shows D and E.

D - Friends should be viewable to everyone. E - Friends should be viewable to everyone.