It says in the Gemarra of Ta'anith, that we are not permitted to speak while we are eating, because there is a fear that the food will go down the windpipe. This ruling in the Gemara has become Halakha. The Rishonim quote it and the Shulhan 'Arukh quotes it without any disagreement.
Rabbenu the Hida in Birkei Yoseph was disturbed. There is no Hakham, he writes, who is particular to follow this ruling. What could be the explanation? Quoting the Eliyah Rabba, who quotes the Perisha, he answers as follows:
At the time when this Halakha came into force, people used to eat while reclining on their left side. Since, nowadays, we do not eat our meals while reclining, this ruling no longer applies. However, since on the night of Pesah (Passover) -- two nights for those of us who live outside the Land of Israel -- we lean when we eat the Massa and drink the Arba' Kosoth (4 cups of wine), we must be particular not to speak while we are eating and leaning.
Indeed, if at any other time of the year we would lean while eating, we would not be permitted to speak then either.
(See Ben Ish Hai, Shana Aleph, Parashath Behar Sinai - Beuqothai, Oth Heh)
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