The moment he heard his name uttered, Loki heard and knew where to find his brother. Immediately he appeared, armed head to toe in his Asgardian armor, armed with his spear in preparation for battle. He arrived invisible, to get an estimate of his surroundings and take advantage of the element of surprise, but the first thing that assalted him were his senses. Particularly, the smell. His nose shriveled at the stench and when he actually viewed the area where he'd appeared, he was revolted. Why would Thor be in this filthy pit?
His attention was then captured by the sight of... Thor? He was almost unrecognizable in the garb of Midgard. Loki could not believe his eyes. Only after the mortal left, did Loki make himself visible, so that it might've seemed as though he had entered through the door. His grin was wide and his uproarious, and malicious laughter filled the room.
"Is this how the mighty god of thunder has fallen? Let me feat my eyes upon this vision so that I may remember it forever, emblazoned upon the front of my memory. Oh, if only the halls of Asgard could see you now, dear brother."