” William asked

“What?” William asked.
“Nothing. I was remembering poor Salvatore. He wanted to perform God knows what magic with that horse, and with his Latin he called him “tertius equi: Which would be the u.”
“The u?” asked William, who had heard my prattle without paying much attention to it.
“Yes, because ‘tertius equi’ does not mean the third horse, but the third of the horse, and the third letter of the word ‘equus’ is u. But this is all nonsense. ...”
William looked at me, and in the darkness I seemed to see his face transformed. “God bless you, Adso!” he said to me. “Why, of course, suppositio materialis, the discourse is presumed de dicto and not de re. ... What a fool I am!” He gave himself such a great blow on the forehead that I heard a clap, and I believe he hurt himself. “My boy, this is the second time today that wisdom has spoken through your mouth, first in dream and now waking! Run, run to your cell and fetch the lamp, or, rather, both the lamps we hid. Let no one see you, and join me in church at once! Ask no questions! Go!”
I asked no questions and went. The lamps were under my bed, already filled with oil, and I had taken care to trim them in advance. I had the flint in my habit. With the two precious instruments clutched to my chest, I ran into the church.
William was under the tripod and was rereading the parchment with Venantius’s notes.
“Adso,” he said to me, “ ‘primum et septimum de quatuor’ does not mean the first and seventh of four, but of the four, the word ‘four’!” For a moment I still did not understand, but then I was enlightened: “Super thronos viginti quatuor! The writing! The verse! The words are carved over the mirror!”
“Come,” William said, “perhaps we are still in time to save a life!”
“Whose?” I asked, as he was manipulating the skulls and opening the passage to the ossarium.
“The life of someone who does not deserve it,” he said. We were already in the underground passage, our lamps alight, moving toward the door that led to the kitchen.
I said before that at this point you pushed a wooden door and found yourself in the kitchen, behind the fireplace, at the foot of the circular staircase that led to the scriptorium. And just as we were pushing that door, we heard to our left some muffled sounds within the wall. They came from the wall beside the door, where the row of niches with skulls and bones ended. Instead of a last niche, there was a stretch of blank wall of large squared blocks of stone, with an old plaque in the center that had some worn monograms carved on it. The sounds came, it seemed, from behind the plaque, or else from above the plaque, partly beyond the wall, and partly almost over our heads.
If something of the sort had happened the first night, I would immediately have thought of dead monks. But by now I tended to expect worse from living monks. “Who can that be?” I asked.
William opened the door and emerged behind the fireplace. The blows were heard also along the wall that flanked the stairs, as if someone were prisoner inside the wall, or else in that thickness (truly vast) that presumably existed between the inner wall of the kitch?en and the outer wall of the south tower.