Messenger box

Messenger box
Wood, embossed and engraved iron, openwork
France, second half of the 15th century
Loaned by Saumur, Château - Museum
Inv No. 919.13.2.189

Exactly what this kind of box was used for remains a mystery: a secret mechanism is hidden inside the lock. Only the owner can open it, but they need more than a key. They need to know how to release the cover by operating an ingenious mechanism (by manipulating part of the decoration, for instance).

FOR KIDS
This box is a real miniature safe! 
Only its owner can open it, using a key that he knows where to slide and then by operating a secret mechanism.
What treasures do you think might have been hidden inside?