Back in more polite times, it was the custom for people to write letters to the rats infesting their homes, asking the rodents to leave before more aggressive measures were taken. From the article "Conjuring Rats," in the Journal of American Folklore (Jan/Mar 1892):
In New England, as well as in other parts of the United States, it is still believed, by certain persons, that if a house is infested with rats, these can be exiled by the simple process of writing them a letter, in which they are recommended to depart, and make their abode in another locality. The letter should indicate precisely the habitation to which they are assigned, and the road to be taken, and should contain such representations of the advantages of the change as may be supposed to affect the intelligence of the animal in question.
The method of delivering the letter was to grease it, roll it up, and push it into the entrance of the rat-hole "in order that it might be duly read, marked, and inwardly digested."