Bocca Di Leone, Venice

 I'm still finding little tidbits about Venice in The Glassblower of Murano novel by Marino Fiorato. Bocca Di Leone (The Lion's Mouth) are embedded in the walls around Venice (one is at the Doge's Palace). Each of these engravings has a wide opening in the mouth of the figure. The purpose of these are to tattle on your neighbors and relatives by inserting a written account of a bad deed or act of treason (the historical equivalent of Twitter). It was important to insert the written document in the correct location as certain "boxes" dealt with specific crimes. The letters were then read by the Council of Ten and punishment ensued. Many of the engravings were destroyed when Napoleon arrived in Venice showing that the island was no longer under Venetian law.

Mark Twain mentions the Lion's Mouth in The Innocents Abroad (free for Kindle):

At the head of the Giant's Staircase, where Marino Faliero was beheaded, and where the Doges were crowned in ancient times, two small slits in the stone wall were pointed out--two harmless, insignificant orifices that would never attract a stranger's attention--yet these were the terrible Lions' Mouths! The heads were gone (knocked off by the French during their occupation of Venice,) but these were the throats, down which went the anonymous accusation, thrust in secretly at dead of night by an enemy, that doomed many an innocent man to walk the Bridge of Sighs and descend into the dungeon which none entered and hoped to see the sun again. This was in the old days when the Patricians alone governed Venice--the common herd had no vote and no voice.