The notion of a "recording demon" was popular in the Middle Ages, and went from sermons to physical representations quickly. Here we see two men gossiping (from St. James' Church, Cristow, Devon), and no matter how close and secretive they are trying to be, right above their heads you can see the recording demon taking notes on what they are saying, to be used against them on Judgment Day.
The idea of a recording demon was known in Egyptian monasteries of the 4th century, and was said to visit churches and monasteries and write down the sins that he observed. This demon was ultimately given a name, Titivillus, and he became responsible to some for causing scribal errors. He was used in sermons about acedia, "spiritual sloth": churchgoers who engaged in idle chatter during the service, and priests who mumbled swiftly through the words of the service in order to get done faster.
Another representation of a demon collecting people's words is the "sack-filling demon" or simply "sack demon." Caesarius of Heisterbach mentions this one: a devil in a high place catching the words of people and putting them in a sack. Jacques de Vitry in his sermons mentions the sack demon with an over-filled sack, difficult to handle with the enormous number of inappropriate things said by folk.
The story of the deacon laughing in church was repeated and embellished over time. One version has the deacon criticized by the priest, who does not believe his story. Later, while asleep, he is exonerated when the Virgin Mary places the scroll of the demon's writings on his chest. The scroll proves to the priest that the deacon was telling the truth.
This is told in a poem by John of Garland, of whom I will say more tomorrow.