Generally speaking, in order for a kinyan – a transfer of ownership – to take place, Jewish law requires gemirut da’at – knowledge and agreement on the part of both the buyer and the seller. It is, therefore, somewhat surprising to hear Rav Huna’s teaching – talyuhu ve-zabein, zevinei zevini – if someone is “hung,” i.e. if he is forced to sell something, the sale takes effect.
In answer to the Gemara’s query of why this would be true, we are told that everyone who sells really is doing it against his will, yet we accept that he agrees to the sale. Here, too, we view him as having accepted the sale.
Obviously, not everyone who sells is unhappy about parting with what he owns; the Gemara is talking about someone who sells personal property because of his financial needs, who reluctantly parts with what he owns. The rishonim explain that even though a businessman wants to sell his merchandise, nevertheless from the case of the individual who sells personal possessions we can learn that even a reluctant agreement is sufficient to create a sale.
The codifiers limit this halakha somewhat. Some rule that the ruling of talyuhu ve-zabein, zevinei zevini applies only in situations where the seller has received payment (according to the Tur, even if he refused to count the money as an indication of protest), and not where he is merely given a written guarantee of payment. At the same time, if the seller writes a statement objecting to the sale, explaining that he is being forced to agree to the sale against his will, but that he remains adamant in his refusal to sell even as he is being forced to accept payment, such a statement will be accepted by the beit din, which will invalidate the sale, returning the object to its original owner and the money to the erstwhile purchaser (see Rambam Hilkhot Mekhira 10:1 and Shulḥan Arukh Ḥoshen Mishpat 151:3 and 205:1).