https://twitter.com/RavBurg/status/1508051825605361670Rav Nochum Partovitz zt"l had two talmidim who were less than diligent. They would spend their time talking by their shtenders. But when Rav Nochum walked in they started screaming "תנו רבנן" as if they had been learning the entire time.
Rav Nochum walked over to the two boys and said, "You are learning Nedarim this year. In the entire Masechta it never says the words תנו רבנן."
Rav Pessin related this story to Rav Chaim zt"l who smiled and immediately responded, "it's true that it never says תנו רבנן but (citing the specific page) it does say דתנו רבנן."
Needless to say Rav Pessin was astounded by the comprehensive grasp that Rav Chaim had over every letter of Shas and later that day told Rav Shteinman zt"l how Rav Chaim responded to the story. Rav Shteinman did not flinch.
Rav Pessin could not understand how Rav Shteinman was not blown away by the story. Rav Shteinman explained, when a person owns even a very large store they know where every tiny item is. When asked they can direct you to the item immediately even if the item is insignificant.
Is the store owner genius? No! It's just that this is their livelihood and so they have dedicated their entire being to it. It matters to them so they master it.
Rav Shteinman explained to Rav Pessin that this is Rav Chaim. All of Torah is his store. To him it is life itself and he has dedicated his entire being to it. It is therefore not surprising in the least that he can instantly recall the one דתנו רבנן in Nedarim.
