de ingenuis moribus et liberalibus adulescentiae studiis, XXXII & XXXIII:
“At these times, when we are unable to employ our leisure outside, reading and books come to our aid. That is, unless we wish to indulge in sleep or to waste away in idle leisure, or even to imitate the custom of the Roman emperor Domitian, who on some days, at certain hours, would withdraw from the company of the world and hunt flies with his iron pen.”
“One of the imperial domestic servants once commented upon the madness of Domitian with a witty joke. At one time, when he was asked whether anyone was in the room with Domitian, the servant responded, ‘Not even a fly,’ as though the emperor had managed to kill them all with his pen.”
in hoc igitur tempus, cum nihil nobis per otium agere foris licebit, lectio librique succurrent. Nisi prorsus somno indulgere aut inerti otio tabescere volemus aut morem imitari Domitiani principis qui singulis diebus, certis horis, secretus ab omnibus stilo ferreo muscas insectabatur.
… eius ipsius Domitiani dementiam e cubiculariis unus urbano scommate notavit. Aliquando enim interrogatus, essetne quisquam cum Domitiano intus, respondit, ‘Ne musco quidem,’ quasi ille stilo suo omnes sustulisset.