It is an animated accessory that can go on top of anything and is located on the chest.
It is a round glass viewport that gives the impression it allows you to view inside the chest.
Just viewable is a red pulsing blob that is a heart.
The rim of the view-port is brass or copper secured with some bolts.
Variations of the mechanical heart allows you to choose a viewport with a lightningbolt inside, a plasma globe, a clockwork showing moving cogwheels or a broken/busted open with broken glass with nothing inside but some wires sticking out.
I don't have the money for this contest, the time nor the skills.
But I do have idea's and this is one I would like to see.
mspaint schetch: