One looked again, and beheld on the wall facing the door a quadrangular hole, about a foot square, with a grating of interlacing iron bars, black, knotted, solid, which formed squares⁠—I had almost said meshes⁠—of less than an inch and a half in diagonal length. The little green flowers of the nankin paper ran in a calm and orderly manner to those iron bars, without being startled or thrown into confusion by their funereal contact. Supposing that a living being had been so wonderfully thin as to essay an entrance or an exit through the square hole, this grating would have prevented it. It did not allow the passage of the body, but it did allow the passage of the eyes; that is to say, of the mind. This seems to have occurred to them, for it had been reinforced by a sheet of tin inserted in the wall a little in the rear, and pierced with a thousand holes more microscopic than the holes of a strainer. At the bottom of this plate, an aperture had been pierced exactly similar to the orifice of a letter box. A bit of tape attached to a bell-wire hung at the right of the grated opening.

If the tape was pulled, a bell rang, and one heard a voice very near at hand, which made one start.