The ancient practice of secret denunciation, which protected the accuser from potential retaliation by the defendant, was widely used in the Republic of Venice. However, it is important to note that this practice was strictly regulated, as denunciations could not be anonymous. The secrecy of the denunciation remained a fundamental condition for the safety of the state. When anonymous reports concerned matters of public interest, they were carefully examined by the Dieci, the highest court responsible for state security, which, if deemed credible, would follow the same procedures as for personally submitted denunciations. In such cases, the defendant had to defend themselves without any legal support, as they had no right to a defense.

The secret denunciation was carried out through special containers, similar to modern mailboxes, distributed throughout the city of Venice, particularly near and inside the Doge's Palace. These containers were meant to collect secret denunciations to be presented to the magistrates. The reports placed in them covered a wide range of offenses, from blasphemy to property crimes, corruption, and electoral fraud. Although many of these denunciations proved to be unfounded, often due to personal jealousy or grudges, others contributed to protecting the very security of the Serenissima.

The name "bocche" (mouths) referred to the appearance of these containers, which were often sculpted to resemble open jaws, with inscriptions indicating the type of denunciation to be inserted. Additionally, the fact that these "mouths" were sometimes designed as a lion's muzzle, recalling the lion of St. Mark, the symbol of the Republic of Venice, gave rise to the term "Bocche di Leone" or "Mouths for Secret Denunciations," in which the accuser would place their message.