The Devil's Dictionary: Incubus
One of a race of highly improper demons who, though probably not wholly extinct, may be said to have seen their best nights. For a complete account of incubi and succubi, including incubae and succubae, see the Liber Demonorum of Protassus (Paris, 1328), which contains much curious information that would be out of place in a dictionary intended as a text-book for the public schools. Victor Hugo relates that in the Channel Islands Satan himself - tempted more than elsewhere by the beauty of the women, doubtless - sometimes plays at incubus, greatly to the inconvenience and alarm of the good dames who wish to be loyal to their marriage vows, generally speaking. A certain lady applied to the parish priest to learn how they might, in the dark, distinguish the hardy intruder from their husbands. The holy man said they must feel his brown for horns; but Hugo is ungallant enough to hint a doubt of the efficacy of the test.