Someone is walking over my grave' seems a rather odd thing for a living person to say when experiencing a sudden shudder, so why is it said? The 18th saying derives from an earlier folk legend that a sudden cold sensation was caused by someone walking over the place that one's grave was eventually going to be.
THE COLD SHIVERING, OR SOMEBODY WALKING OVER MY GRAVE!
One moonlight evening, in the gardens at Naples, some four or five friends, ladies, and gentlemen, were seated under a tree, listening, in the intervals of conversation, to the music which enlivened that gay and favorite resort of an indolent population. Of this little party was an English lady, who had been the life of the whole group, but who, for the last few moments, had sunk into a gloomy and abstracted reverie. One of the party observed this sudden depression of spirits, and tapping his fair friend gently on the shoulder, said, "what ails you, Lady fair? are you ill? You have grown quite pale—you tremble. Is it a sudden chill? You had better go home: these Italian nights are often dangerous to English Constitutions." "No, I am well now; it was a passing shudder! I cannot account for it myself." Another of the party, turning to the lady, with a steadfast [sic] countenance, quickly remarked, "I think I understand what you mean, and perhaps," he added with rather a seriocomic smile, "I can explain it better than yourself." Here turning to the others, he added, "you must have often felt, my friends, each, and all of you, especially when sitting alone at night, a strange and unaccountable sensation of coldness, and awe, creep over you; your blood curdles, and the heart stands still; the limbs shiver, the skin puckers, like that of a goose, and with this "horripilation" the hair bristles; you are afraid to look up,—to turn your eyes to the dark corners of the room; you have a horrible fancy that something unearthly is at hand; presently the whole spell, if I may so call it, passes away, and you are ready to laugh at your own weakness. Have you not often felt what I have thus imperfectly described? if so, you can understand what our fair friend has just experienced, notwithstanding even the delights of this magical scene, and amid the balmy whispers of a July night." "Yes indeed," she replied, evidently much surprised, "you have defined exactly the nature of that shudder which came over me. But tell me, how could my manner be so faithful an index to my real impressions?" "I know the signs of the Visitation," returned the friend, gravely, "as well as I know thy smiles!—they are not to be mistaken." And, moreover, all present declared that they could comprehend, and had felt, what had been thus described. "According to one of our national superstitions," said one of the parties, who had first addressed the lady, "the moment you so feel your blood creep, and your hair stand on end, someone is walking over your grave, however far distant it may be. There are in all lands different superstitions to account for so common an occurrence:—The African savage, whose imagination is darkened by the hideous rites of his gloomy idolatry, believes that the Evil Spirit is pulling him by the hair; so do the grotesque and the terrible mingle with each other." "It is evidently a mere physical accident—a derangement of the stomach—a chill of the blood," said another gentleman. "Then why is it always coupled," asked another, "in all nations, with some superstitious presentiment, or terror? some connexion between the material frame, and the supposed world, without us? For my part I think——" "Ay, what do you think?" asked the lady, curiously. "I think," said the gentleman, "that it is the repugnance and horror, our more than human elements recoil from something, really invisible, but antipathetic to our own nature; and from a knowledge of which we are happily secured, by the imperfection of our senses." "You are a believer in spirits, then?'" said another, with a smile. "Nay, it was not precisely of spirits that I spoke! but there may be forms of matter, as invisible and impalpable to us, as the animalculæ in the air we breathe—in the water that plays in yonder basin, rising from the fountain spring. Such beings may have passions, and powers like our own—as the animalculæ to which I have compared them. The monster, that lives and dies in a drop of water—carnivorous—insatiable—subsisting on creatures minuter than himself—is not less deadly in his wrath, or less ferocious in his nature, than the tiger of the desert. There may be things around us, that would be dangerous and hostile to men, if Providence had not placed a wall between them and us, merely by different modifications of matter." "And, think you that wall never can be removed?" asked the lady, quickly; "are impediments so strongly fixed? Are the traditions of the Sorcerer, and the Wizard, universal and immemorial as they are, merely fables?" "Perhaps, yes! perhaps, no!" answered the friend indifferently. "But who, in an age in which reason has chosen her proper bounds, would be mad enough to break the partition that divides him from the boa and the lion?—to repine at, and to rebel against the law, which confines the whale and the shark to the great deep? Enough of these, as well of other idle speculations!" Such can only exist in the fantasy of Rosicrucians.
The Dutch too held that folk belief, according to this extract from Dutch Folk-lore, by an anonymous correspondent from Amsterdam, published in Notes and Queries (George Bell – London, England) of Saturday 17th May 1851:
If you feel of a sudden a shivering sensation in your back, there is somebody walking over your future grave.
A variant phrase was used in The Knickerbocker, or New York Monthly Magazine (John Allen – New York City, N.Y., USA) of March 1843:
A lady […] observed, in the words of an old saying, and with a slight shudder as from cold, 'I feel as if a goose were walking over my grave;' the origin, we may suppose, of the term 'cold goose-pimple.'
That variant originated in Ireland, according to The Massachusetts Spy (Worcester, Massachusetts, USA) of Wednesday 9th May 1849:
There is a saying common in Ireland when one feels a sudden chill that acts upon the skin, 'I feel as if a goose were walking over my grave.'
IN FRENCH
The equivalent phrase exists in French as on march sur ma tombe, somebody is walking over my grave.
In the following from Revue des traditions populaires (Société des traditions populaires au Musée d'ethnographie du Trocadéro – Paris) of March 1895, it seems that the phrase does not refer to the future grave, but to the 'past' grave, of someone who "believes to have already lived":
Le frisson, l'âme, les rêves. — Un soir, dans le salon de l'hôtel Néva, au milieu du silence d'une partie de cartes en famille, une parisienne dit tout-à-coup, très haut : « On marche sur ma tombe ». — Ebahissement général, le jeu est arrêté. — Alors cette dame, après avoir expliqué qu'elle venait d'éprouver un frisson, m'avoue qu'elle croit avoir déjà vécu et que l'impression ressentie provient de ce que quelqu'un a marché sur sa tombe. — A ce propos, plusieurs personnes disent à leur tour qu'elles pensent que leur âme a déjà habité d'autres corps et que les rêves sont des visions de leur existence passée, présente ou future.
(Cannes, février 1895, Comm. de M. A. Certeux).
translation:
The shudder, the soul, the dreams. — One evening, in the lounge of the Néva hotel, in the midst of a family card game, a Parisienne said suddenly, very loudly: "Somebody is walking over my grave". — General astonishment, the game is stopped. — Then this lady, after explaining that she had a moment before felt a shudder, confesses to me that she believes to have already lived and that the impression felt comes from the fact that somebody has walked over her grave. — In this connection, several persons say in their turn they think that their soul has already inhabited other bodies and that their dreams are visions of their past, present, or future existence.
(Cannes, February 1895, Communication from M. A. Certeux).
Note: The proverb that Lord Sparkish uses was quoted as already common around 1460 in The First Shepherds' Play, from the Towneley mystery plays:
It is sayde full ryfe,
'A man may not wyfe
And also thryfe,
And all in yere.'
in modern English:
It is commonly said,
'A man may not marry
And also prosper,
And all in a year.'
The old folk belief is recorded by the Yorkshire novelist Harriet Parr, who also used a pseudonym, that of Holme Lee, in Basil Godfrey's Caprice, 1868:
Joan shuddered - that irrepressible convulsive shudder which old wives say is caused by a footstep walking over the place of our grave that shall be.
The expression is sometimes found in the form of 'a goose (or occasionally, a rabbit) walked over my grave. These are later and chiefly American variants and the 'goose' version at least appears to be a back-formation, derived from 'goosebumps/goose pimples' which are associated with a sudden feeling of chilliness.
The modern-day scientific explanation for sudden unexplained shuddering and for goose pimples is that they are caused by a subconscious release of the stress hormone adrenaline. This may be as a response to coldness or an emotional reaction to a poignant memory. Fanciful it may be, but somehow, I prefer the medieval version.