"The whole circuit of its walls did not exceed twenty-five yards. For some minutes this fact occasioned me a world of vain trouble; vain indeed! for what could be of less importance, under the terrible circumstances which environed me, than the mere dimensions of my dungeon"(229-233). Poe wasn't terrified, but he was more interested about how he pictured room wron. Poe is trying to remain calm in his situation and distracting himself with a bit of humour.
"With the particles of the oily and spicy viand which now remained, I thoroughly rubbed the bandage wherever I could reach it; then, raising my hand from the floor, I lay breathlessly still"(415-417). Poe's thinking allowed him to set himself free from the pendulum using the rats to cut his bindings. With death near moments away, elongating his close demise created suspense of his escape. In his situation, he was able to stay calm and not let himself get killed.
"I shrank back—but the closing walls pressed me resistlessly onward. At length for my seared and writhing body there was no longer an inch of foothold on the firm floor of the prison" (508-511). Poe is about to die, or the build up to this moment makes it seem that way. The dragging on about the walls closing in and the pit coming closer to him, will he die? We find out that he was saved, the suspense has ended. A bit unexpected for the build up, it felt refreshing that he was able to survive this nightmare.