[The ideal conditions for this kind of thing were an empty, silent room. However, having been in battle before, Harry knew ideal conditions were a luxury more often than not. Therefore, he had trained his mind to go blank - not its usual state, contrary to popular beliefe - whenever he needed it.
He focused the energy inside the circle to link the piece of oni to its source. Soon enough, he felt a slight pull. Harry got up and broke the circle with his foot before stepping out. He only needed to follow that pull to its origin]