Rabin and Abbaye were sitting in front of Rabana Nehemia, the Exilarch's brother. They saw that he was wearing silk. Rabin said to Abbaye, "That's the kalakh that the Mishnah mentions!" He said to them, "We call it sira paranda."
Spoken words are central to Jewish thought, religion, and practice. Our Sages believed that the world was created with divine utterances and their Torah was transmitted from mouth to ear. The word mishnah probably means recited teaching. The Mishnah was almost certainly imported to Babylonia in an entirely oral form. But what would happen if the meaning of an obscure Hebrew word in the Mishnah was forgotten? This is exactly the situation that motivates Rabin and Abbaye's Aramaic dialog in the above conversation.
The Mishnah (Shabbat 2:1) prohibits the use of kalakh as a wick in the Shabbat lights. Apparently, it is a material that will not take up fire quickly but will simply burn, smoke, and then go rapidly out. The problem is that the Sages in Babylonia are unfamiliar with this particular word. What is kalakh? Rabbin has been to the land of Israel for study and when he sees the aristocratic brother of the Exilarch (the political leader of the Jews under Persian rule) a memory is triggered by his fancy dress: "That material that he is wearing, that's kalakh!" Rabana Nehemia, brought up in proximity to the Persian court, tells them: "We call it (in Persian) sira paranda." Note that at least three languages are at play in this passage, and I have added a fourth (English) by translating the story. Though Rabin, Abbaye, and Rabana Nehemia are all from different backgrounds and speak a variety of languages, they are united by their love of Torah and their commitment to beautifying Shabbat with long-lasting lights.