Pig in a poke
The idioms pig in a poke and sell a pup (or buy a pup) refer to a confidence trick originating in the Late Middle Ages, when meat was scarce, but cats and dogs (puppies) were not. The idiom pig in a poke can also simply refer to someone buying a low-quality pig in a bag because he or she did not carefully check what was in the bag.
The scheme entailed the sale of a suckling pig or pup in a poke (bag). The bag would actually contain a cat or dog (not particularly prized as a source of meat), which was sold to the victim in an unopened bag. The French idiom acheter (un) chat en poche (to buy a cat in a bag) refers to an actual sale of this nature, as do many European equivalents, while the English expression refers to the appearance of the trick.
Relation to other idioms and expressions 
The English colloquialisms such as turn out to be a pig in a poke or buy a pig in a poke mean that something is sold or bought without the buyer knowing its true nature or value, especially when buying without inspecting the item beforehand. The phrase can also be applied to accepting an idea or plan without a full understanding of its basis. Similar expressions exist in other European languages, most of them referring to the purchase of a cat in a bag.
The advice being given is 'don't buy a pig until you have seen it'. This is enshrined in British commercial law as 'caveat emptor' - Latin for 'let the buyer beware'. This remains the guiding principle of commerce in many countries and, in essence, supports the view that if you buy something you take responsibility to make sure it is what you intended to buy.
A poke is a sack or bag. It has a French origin as 'poque' and, like several other French words, its diminutive is formed by adding 'ette' or 'et' - hence 'pocket' began life with the meaning 'small bag'. Poke is still in use in several English-speaking countries, notably Scotland and the USA, and describes just the sort of bag that would be useful for carrying a piglet to market.
A pig that's in a poke might turn out to be no pig at all. If a merchant tried to cheat by substituting a lower value animal, the trick could be uncovered by letting the cat out of the bag. Many other European languages have a version of this phrase - most of them translating into English as a warning not to 'buy a cat in a bag'. The advice has stood the test of time and people have been repeating it in one form or the other for getting on for five hundred years, maybe longer.
|Bulgarian||да купиш котка в торба||to buy a cat in a bag|
|Catalan||Donar/Prendre gat per llebre||to give/to take cat instead of hare|
|Chinese||挂羊头卖狗肉||sell dog meat as mutton|
|Croatian||kupiti mačka u vreći||to buy a cat in a sack|
|Czech||koupit zajíce v pytli||to buy a hare in a sack|
|Danish||at købe katten i sækken||to buy the cat in the sack|
|Dutch||een kat in een zak kopen||to buy a cat in a sack|
|Estonian||ostma põrsast kotis||to buy a piglet in a sack|
|French||acheter un chat dans un sac
acheter chat en poche
|to buy a cat in a bag|
|Finnish||ostaa sika säkissä||to buy a pig in a sack|
|German||Die Katze im Sack kaufen||to buy the cat in the sack|
|Greek||αγοράζω γουρούνι στο σακκί||to buy a pig in a sack|
|Hebrew||חתול בשק||cat in a sack|
|Hungarian||zsákbamacska||cat in a sack|
|Icelandic||að kaupa köttinn í sekknum||to buy the cat in the sack|
|Indonesian||kucing dalam karung||cat in a sack|
|Italian||comprare a scatola chiusa||to buy a sealed can|
|Irish||ceannaigh muc i mála||buying a pig in a bag|
|Latvian||pirkt kaķi maisā||to buy a cat in a sack|
|Lithuanian||pirkti katę maiše||to buy a cat in a sack|
|Luxembourgish||d'Kaz am Sak kafen||to buy the cat in a sack|
|Macedonian||да купиш мачка во вреќа||to buy the cat in the sack|
|Norwegian||kjøpe katta i sekken||to buy the cat in the sack|
|Polish||kupić kota w worku||to buy a cat in a sack|
|Portuguese||comprar gato por lebre||to buy a cat instead of a hare|
|Romanian||cumperi mâța în sac||to buy the cat in the bag|
|Russian||купить кота в мешке||to buy a cat in a sack|
|Spanish||dar gato por liebre||to give a cat instead of a hare|
|Spanish||hay gato encerrado||there is a cat shut inside|
|Serbian||купити мачку у џаку||to buy a cat in a sack|
|Slovak||kúpiť mačku vo vreci||to buy a cat in a sack|
|Slovene||kupiti mačka v žaklju||to buy a cat in a sack|
|Swedish||köpa grisen i säcken||to buy the pig in the sack|
|Welsh||prynu cath mewn cwd||to buy a cat in a bag|
This trick also appears to be the origin of the expression "let the cat out of the bag", meaning to reveal that which is secret (if the would-be buyer opened the bag, the trick would be revealed). However, there is some reason to believe that the term "letting the cat out of the bag" originates in the British Royal Navy of Admiral Nelson's time or earlier and refers to the act of removing the so called "Cat o' Nine Tails", a form of whip or scourge used in punishment, from a bag. This is also believed to be the origin of the term "No room to swing a cat" according to the staff of HMS Victory and refers to the low headroom on the gundecks, where punishment using the "Cat" was performed.
In the April 1929 edition of the literary magazine London Aphrodite, a story by Rhys Davies, titled "A Pig in a Poke", was published, in which a Welsh collier takes a woman from London for his wife and regrets it. (Boulton 1993: p. 278)
- pig in a poke at YourDictionary.com
- pup at Longman Dictionary of Contemporary English
- be sold a pup at The Free Dictionary
- pig in a poke at IdiomDictionary.com
- Brewer, Dictionary of Phrase and Fable, 1898.
- Let the cat out of the bag on The Phrase Finder
- Boulton, James T. (1993). The Letters of D.H. Lawrence. Volume VII: November 1928 – February 1930. Cambridge: Cambridge University Press.
- E. Cobham Brewer, Dictionary of Phrase and Fable. 1898.
- Funk, Charles Earle, A Hog on Ice: & Other Curious Expressions. HarperResource, 2002. ISBN 0-06-051329-2.