Our Gemara on Amud Aleph tells us that Rav Sheshes was able to tell from the sound the pestle made, which substance was being grinded and the manner in which the pestle was being held. 

An additional factor not mentioned in this Gemara is that Rav Sheshes was blind (Berachos 58a), and so like many persons with some disabled sense, we may surmise that another sense takes over and compensates. Rav Sheshes’ hearing was stronger to augment his abilities, and thus he was able discern many details about the mill even without yet entering his home. He also had an extraordinary memory, as he would review all his learning every 30 days (Pesachim 68b). Perhaps this too was a compensation for his blindness.

A fascinating historical note about Rav Sheshes can be found in the commentary of Rabbenu Gershom at the end of Menachos (110a). He states the fact that the two students of Rav who were both blind, Rav Yosef and Rav Sheshes, is not a coincidence. Rav was particularly careful in shemiras einayim and two of his loyal students desired so strongly to live up to their master’s standard, that they became blind by divine Providence. Even more confusing is a tradition noted by the Chida in (Pesach Eynayim Menachos ibid) and recorded in Seder Hadoros (under entry of Rav Yosef) that Rav Sheshes and Rav Yosef deliberately damaged their eyesight in order to live up to Rav’s standard. Such behavior is difficult to understand, and I won’t even try, because I could not possibly explain it. What I will say is that we can be impressed and inspired as to how much they desired to be free from the distractions of ordinary daily sights, even though such extreme actions are beyond what ordinarily is allowed.