The whole of this very material cult depended upon the assumption--which was sometimes distinctly expressed--that the soul of the dead is capable of receiving, and is in need of, a physical satisfaction from the gifts made to it.[108\5] It is consequently, not thought of as deprived of the power of sense-perception. Even in the grave it can feel what is going on in its neighbourhood.[109\5] It is not a good thing to attract its attention; it is best to pass by the graves of the dead in silence.[110\5] The common people thought of the dead, according to a famous phrase of Plato's, as "hovering" suspended over their graves, the site of their cult.[111\5] The pictures on the Attic oilflasks illustrate this belief, for they represent the souls of the dead flying above the grave-monument, and the diminutive size of these winged figures is evidently intended to represent their somewhat contradictory immaterial materiality, and to express their invisibility for mortal eyes.[112\5] Sometimes, indeed, the souls become visible, and then, like the underworld gods and the Heroes, they prefer the shape of a snake.[113\5] Nor are they absolutely bound to the immediate neighbourhood of the grave; they sometimes revisit their old habitations among the living, and not only on those days of the dead in the month Anthesterion. The Greeks, like other people, were acquainted with the custom of allowing what fell to the ground to lie there undisturbed for the spirits that hovered about the house to carry away if they liked.[114\5] The dead man's spirit, being thus invisibly present, can overhear if anyone speaks ill of it: either with the idea of defending the helpless, or, on the contrary, to avoid incurring the wrath of invisible but potent spirits, a Solonian law forbade abusive language to be addressed to a dead man. That is the real meaning of the old warning _de mortuis nil nisi bene_, as popular belief understood it. The descendants of a dead man were bound to prosecute anyone who slandered their ancestor:[115\5] this also is among the religious duties owed by the living to the soul of the dead. § 3