Library Hippolytus Refutation of All Heresies
Book 4
Chapter 40: Trick with the Liver
And they exhibit a liver seemingly bearing an inscription in this manner. With the left hand he writes what he wishes, appending it to the question, and the letters are traced with gall juice and strong vinegar. Then taking up the liver, retaining it in the left hand, he makes some delay, and then it draws away the impression, and it is supposed to have, as it were, writing upon it.
English translation by J.H. MacMahon, in Ante-Nicene Fathers, Vol. V (eds. Alexander Roberts and James Donaldson; Buffalo: Christian Literature Publishing Co., 1886). Public domain. Digital text via New Advent Church Fathers.