"I had experiments carried out," he explained languidly, "with the
object of discovering methods and means for rendering walls and
ceilings capable of effective resistance to sound transmission.
One of the methods devised involved the use under the ceiling or
parallel to the wall, as the case might be, of a network of wire
stretched tightly by means of pulleys in the adjacent walls and
not touching at any point the surface to be protected against
sound. Upon the wire network is plastered a composition formed of
strong glue, plaster of Paris, and granulated cork, so as to make
a flat slab, between which and the wall or ceiling is a cushion of
confined air. The method is good in two respects: the absence of
contact between the protective and protected surfaces and the
colloid nature of the composition used. I have gone into the thing
at length because it will make all the more remarkable what I am
about to tell you."

Kennedy had been listening attentively. As Brixton proceeded I had
noticed Kennedy's nostrils dilating almost as if he were a hound
and had scented his quarry. I sniffed, too. Yes, there was a faint
odour, almost as if of garlic in the room. It was unmistakable.
Craig was looking about curiously, as if to discover a window by
which the odour might have entered. Brixton, with his eyes
following keenly every move, noticed him.

"More than that" he added quickly, "I have had the most perfect
system of modern ventilation installed in this room, absolutely
independent from that in the house."

Kennedy said nothing.