The interior view of the secret denunciation letterbox, with two sets of doors into the box, the outer one with a lock. The opening to the outside is visible through the open doors.

A letterbox in the wall of the Doge's Palace, Venice, in the form of a grimacing face with an open mouth, which is the opening. Under is written "Secret denunciations against anyone who will conceal favours and services or will collude to hide the true revenue from them." A place to anonymously denounce anyone guilty of peculation.