The Prophet ordered his followers to kill serpents and scorpions if they intruded at prayers; but on other occasions he seems to have required first to admonish them to depart, and then, if they remained, to kill them. The Doctors, however, differ in opinion whether _all_ kinds of snakes or serpents should be admonished first, or whether _any_ should; for the Prophet, say they, took a covenant of the Jinn [probably after the above-mentioned command], that they should not enter the houses of the faithful: therefore, it is argued, if they enter, they break their covenant, and it becomes lawful to kill them without previous warning. Yet it is related that ´Aïsheh, the Prophet's wife, having killed a serpent in her chamber, was alarmed by a dream, and fearing that it might have been a Muslim Jinnee, as it did not enter her chamber when she was undressed, gave in alms, as an expiation, twelve thousand dirhems (about £300), the price of the blood of a Muslim.[40] The Jinn were said to appear to mankind most commonly in the shapes of serpents, dogs, cats, or human beings. In the last case, they are sometimes of the stature of men, and sometimes of a size enormously gigantic. If good, they are generally resplendently handsome: if evil, horribly hideous. They become invisible at pleasure, by a rapid extension or rarefaction of the particles which compose them, or suddenly disappear in the earth or air or through a solid wall. Many Muslims in the present day profess to have seen and held intercourse with them:--witness the following anecdote, which was related to me by a Persian with whom I was acquainted in Cairo, named Abu-l-Ḳásim, a native of Jeelán, then superintendent of Moḥammad ´Alee's Printing-office at Booláḳ.