In the following experiment this sound was used with great effect. Nellie's cage occupied a place in my study near my desk. She would stay awake at night as long as the light was kept burning, and as I have always kept late hours, I did not violate the rule of my life in order to give her a good night's rest. About two o'clock one morning, when I was about to retire, I found Nellie wide awake. I drew my chair up to her cage, and sat watching her pranks as she tried to entertain me with bells and toys. I tied a long thread to a glove, which I placed in a corner of the room at a distance of several feet from me, but without letting her see it. I held one end of the string in my hand, I drew the glove obliquely across the floor towards the cage. When I first tightened the string, which I had drawn across one knee and under the other, the glove moved very slightly, and this her quick eye caught at the very first motion. Standing almost on tip-toe, her mouth half open, she would peep cautiously at the glove, and then in a low whisper would say "e-c-g-k"! And every second or so would repeat it, at the same time watching me, to see whether I was aware of the approach of this goblin. Her actions were almost human, while her movements were as stealthy as those of a cat. As the glove came closer and closer she became more and more demonstrative, and when at last she saw the monster climbing up the leg of my trousers, she uttered the sound aloud and very rapidly, and tried to get to the object, which she evidently thought was some living thing. She detected the thread with which I drew the glove across the floor, but seemed in doubt as to what part it played in this act. I saw her eyes several times follow the thread from my knee to the glove, but I do not think she discovered what caused the glove to move. Having done this for a few times, however, with about the same result each time, I relieved her anxiety and fright by allowing her to examine the glove, which she did with marked interest for a moment and then turned away. I tried the same thing over again, but failed to elicit from her the slightest interest after she had examined the glove. [Sidenote: SOUND OF WARNING]