But though the footprint is the most obvious it is not the only impression made by the body through which magic may be wrought on a man. The aborigines of south-eastern Australia believe that a man may be injured by burying sharp fragments of quartz, glass, and so forth in the mark made by his reclining body; the magical virtue of these sharp things enters his body and causes those acute pains which the ignorant European puts down to rheumatism.​[797] Sometimes they beat the place where the man sat with a pointed stick of the he-oak (_Casuarina leptoclada_), chanting an appropriate song at the same time; the stick will enter his person and kill him, provided the place operated on is still warm with the heat of his body.​[798] At Delena, in British New Guinea, a man will sometimes revenge himself on a girl who has rejected his love by thrusting the spine of a sting-ray into the spot where she has been sitting; afterwards he puts it in the sun for a day or two and finally heats it over a fire. In a couple of days the girl dies.​[799] The natives of Tumleo, an island off German New Guinea, efface the marks they have left on the ground where they sat, lest magic should be wrought on them thereby.​[800] Before they leave a camping-place some of the natives of German New Guinea are careful to stab the ground thoroughly with spears, in order to prevent a sorcerer from making any use of a drop of sweat or any other personal remains which they may chance to leave behind.​[801] We can now understand why it was a maxim with the Pythagoreans that in rising from bed you should smooth away the impression left by your body on the bed-clothes.​[802] The rule was simply an old precaution against magic, forming part of a whole code of superstitious maxims which {p214} antiquity fathered on Pythagoras, though doubtless they were familiar to the barbarous forefathers of the Greeks long before the time of that philosopher.​[803] To ensure the good behaviour of an ally with whom they have just had a conference, the Basutos will cut and preserve the grass on which the ally sat during the interview.​[804] Probably they regard the grass as a hostage for the observance of the treaty, since through it they could punish the man who sat on the grass if he should break faith. Moors who write on the sand are superstitiously careful to obliterate all the marks they made, never leaving a stroke or a dot in the sand when they have done writing.​[805] Another of the so-called maxims of Pythagoras bade people in lifting a pot always to smooth away the imprint it left on the ashes.​[806] So in Cambodia they say that when you lift a pot from the fire you should not set it down on the ashes; but that, if you must do so, you should be careful, in lifting the pot from the ashes, to efface the impression it has made. Otherwise they think that want will knock at your door.​[807] But this seems to be an afterthought, devised to explain a rule of which the original meaning was forgotten.