These uneducated soldiers ascribe supernatural unhuman qualities to the invaders. A little further they suspect that the French military commander Napoleon possesses shape-shifting and undead capabilities:
He turns into a bird in his hands and flies away. And there’s no way
of killing him either. [...] If he fell into my hands, when I’d caught
him I’d bury him in the ground with an aspen stake to fix him down.
Historian Alexander Tchoudinov in his paper “С КЕМ ВОЕВАЛ РУССКИЙ МУЖИК В 1812 ГОДУ?
ОБРАЗ ВРАГА В МАССОВОМ СОЗНАНИИ” (Who was Russian Peasant at War with in 1812? The Image of the Enemy in the Mass Consciousness) tries to investigate his subject by studying Russian folklore. (Here are popular presentations and PDF. I’ll give some translated excerpts.)
In the XVIII century folk culture “French” was mostly a mark of the difference between the life of the Russian nobility and peasants:
In other words, "French" was perceived as "foreign" not so much
because it was "non-Russian" but because it belonged to "alien"
The author mentions a speech by a rayok performer who describes peculiar dishes that noblemen eat:
Strange for the Russian ear, the culinary terms like "menu" […]
"jelly", "torte" and the no less outlandish dishes which had French
origin, like a pie stuffed with frog legs, emphasize the striking
difference in the lifestyle of the Russian gentry...
So here's the role of food in constructing the difference.
Tchoudinov says that the invasion of 1812 was an unprecedented event for Russians. Since they couldn’t rely on their experience they had to resort to an existing archetype in the folklore which was heavily influenced by the Mongol invasion. This archetype had three features. The enemy is anti-Christian, predatory and dehumanized (i.e. shown as inhumanly violent):
in the collective memory of the "silent majority" of Russian society
for centuries there was a single, syncretic image of a foreign enemy,
which possessed such pronounced specific features as hostility to
Christianity, predatory nature, inhumanity, but at the same time
deprived of any clearly defined ethnic identity. Collective memories
of foreign enemies appearing in different historical epochs turned out
to be integrated into something whole, becoming part of a single
archetype of the Enemy that practically did not change over time.
So the dehumanizing discourse was applied to the French. In the folk songs they want to skin people alive, take all the women and turn churches into horse stables. The motive of Tatars turning churches into stables appears even in old epic poems. The problem is that
French soldiers, indeed, often stayed in churches, bringing their
horses there as well. They did not put any anti-religious meaning into
such actions, but simply followed their accepted practice: tents were
not used in the French army
OK, if the French didn’t commit all these atrocities, then who did? Well…
The way the Russian peasants treated the captured French made
enlightened contemporaries recall the darkest pages of medieval
history. In the villages, prisoners were tortured, burned and buried
alive. [..]The English General Robert Thomas Wilson, seconded to the
Russian army, testifies:
Not far from Vyazma, fifty Frenchmen were wildly burned alive. In
another village, fifty people are buried alive. But all these terrible
acts of cruelty are not the worst…
Then the author describes some very bad act of ritualized violence. Tchoudinov says:
The anti-Christian and dehumanized nature of the enemy placed him
outside of morality and compassion, allowing and even prescribing
behavior towards him that a Christian would hardly allow himself with
his own kind
Some authors, however, believe that official propaganda should be blamed for this cruelties. The paper “Партизаны и народная война в 1812 году” (Partisans and the People's War in 1812) by A.I. Popov (PDF here) mentions the peasant saying:
"А вот вишь ты, — сказал крестьянин, — наловили мы это их,
французов-то, десятка два и стали думать, что бы с ними наделать... и
приговорили миром побить их". Тут он приостановился и, подумав, со
вздохом продолжал: " Оно точно того, если бы он на тебя с ножом лез,
ничего бы... а то смотрит как баран; как тут быть-то? Француз не
баран, а все же человек, враг только, землю разорил"» [...]. Даже
церковная пропаганда не могла затуманить в сознании мужика того, что
он поступал не по христиански, убивая безоружных людей.
"But you see," said the peasant, "we caught them, the French, about
two dozen and began to think what to do with them... and sentenced
them to be beaten by the people." Here he paused and, after thinking,
continued with a sigh: "It's definitely worth it, if he jumps on you
with a knife, it would be nothing... and then he looks like a sheep;
what to do here? The Frenchman is not a sheep, but still a man, an
enemy only… and has ravaged our land" [...] Even church propaganda
could not obscure in the mind of the peasant that he was acting
un-Christian, killing unarmed people.
In the next chapter, War and Peace characters meet two French soldiers. They give to one of them some hot porridge. He really appreciates the porridge. (One might turn back to the ‘Fed ’em like gentry’ and make a connection.)