When you have made a serious error and need to acknowledge it humbly, it is highly probable that the expression you use to describe the process has something to do with food.
The best-known traditional expression of this type in the US is to eat crow. The origin seems fairly obvious: the meat of the crow, being a carnivore, is presumably rank and extremely distasteful, and the experience is easily equated to the mental anguish of being forced to admit one’s fallibility. But you may understand that my desire for accuracy has not led me so far as trying the experiment for myself, though taking a line through rook pie, which I tried once at an over-enthusiastic historical reconstruction, it seems a reasonable assumption. We need someone like the eccentric Victorian surgeon Frank Buckland, founder of the London Acclimatisation Society — dedicated to introducing useful new plants and animals into countries where they were unknown — whose hobby was eating his way through the animal kingdom, trying out delicacies such as roast giraffe and elephant trunk soup. He once returned from holiday to find that a leopard at the London Zoo had died and been interred in a flower bed; seizing a spade, he immediately dug it up to try it. He is on record as remarking that “the very worst thing he ever ate was a mole”, but I can’t find out what he thought of crows. Volunteers to make empirical observations should form an orderly queue.
An article published in the Atlanta Constitution in 1888 claims that, towards the end of the war of 1812, an American went hunting and by accident crossed behind the British lines, where he shot a crow. He was caught by a British officer, who, complimenting him on his fine shooting, persuaded him to hand over his gun. This officer then levelled his gun and said that as a punishment the American must take a bite of the crow. The American obeyed, but when the British officer returned his gun he took his revenge by making him eat the rest of the bird. This is such an inventive novelisation of the phrase’s etymology that it seems a shame to point out that the original expression is not recorded until the 1850s, and that its original form was to eat boiled crow, whereas the story makes no mention of boiling the bird.
The British English equivalent is eating humble pie, which contains two ideas rolled in together, a portmanteau dish. The original umbles were the innards of the deer: the liver, heart, entrails and other second-class bits. It was common practice in medieval times to serve a pie made of these parts of the animal to the servants and others who would be sitting at the lower tables in the lord’s hall. Pepys mentions it in his diary for 8 July 1663: “Mrs Turner came in and did bring us an Umble-pie hot out of her oven, extraordinarily good”. However, it seems it was not until the nineteenth century that the expression humble pie appeared in the sense we now know, and some have reasoned that it did so as a deliberate play on words. If so, it was a very small play. The word umbles is a variant form of an old French term noumbles, (originally from Latin lumulus, a diminutive of lumbus, from which we also get loin and lumbar); umbles seems to be derived from numbles by the process called metanalysis which, for example, turned a norange into an orange; umbles also sometimes appeared in medieval times and later in the form humbles. Contrariwise, the word humble (originally from the Latin humilem from which we also get humility) was frequently spelt and pronounced “umble” from medieval times right down to the nineteenth century. So the figurative sense of umble pie could have appeared at almost any time since the medieval period; indeed, so close is the association that it is surprising that the OED’s first citation dates only from 1830.
The phrase to eat dirt, first attested in the 1850s, expresses the same idea as to eat crow and to eat humble pie. The oldest of them, and most probably the source of all the others, is to eat one’s words, which first appears in print in 1571 in one of John Calvin’s tracts, on Psalm 62: “God eateth not his words when he hath once spoken”.
Whilst we are on the subject of consuming unconsumables: the expression to eat one’s hat, expressing one’s complete confidence in the outcome being described — “if that horse doesn’t win, I’ll eat my hat” — dates in this form only from 1836, when it appeared in Charles Dickens’ Pickwick Papers: “If I knew as little of life as that, I’d eat my hat and swallow the buckle whole”. According to the OED, the phrase used to appear sometimes in the form eat old Rowley’s hat, though I’ve never seen it and the OED has no citations for it. Old Rowley was the name of Charles II’s favourite horse, a name that was transferred to the monarch himself, though why his hat should be especially favoured in idiomatic history is a mystery. There were earlier expressions invoking one’s hat in support of some assertion: by my hat (which turns up in Love’s Labour Lost), my hat to a halfpenny, and I’ll bet a hat, so it is possible that Dickens’ formation may draw on one or other of these and on the then newish eat humble pie.
To eat one’s heart out, in its sense of suffering extreme grief, is a vivid figurative description which also evokes the often intensely physical symptoms of worry. It actually predates the English language, since it turns up in Homer’s Iliad (about 850 BC) and in writings by Pythagoras four hundred years later. Some proverbial sayings have a very long history indeed.