Houdini brought the “east Indian Needle Trick” from the obscurity of sideshows to popular culture in the early 1900s. In this trick, Houdini swallows 50 to 100 needles, 20 yards of thread and brings them all up threaded, after his mouth and throat have been inspected by a committee. He begins by placing the needles and thread on his tongue and appears to swallow them. To perform this trick, Houdini would simply place a length of thread already threaded with needles and place them between his lips and gums before his mouth was examined. By tying a note on each side of the needle, a little “play” was allowed, so that the needles were loose, appearing to be normally threaded. This prevented any real danger of having the needles coming loose from the thread, which could have injured Houdini. At this point, Houdini’s job was simply to deceive the committee. This required a great deal of thought and skill. In showing his mouth, he would draw his upper and lower lips away from his gums and teeth. Most suspicion was directed toward the back portion of the upper gums and Houdini would simply draw his cheeks wide with his little fingers to give a thorough view of the area. In drawing his lower lips and pulling his cheeks outward, his fingers would cover the needles hidden by his lower lip. He could also move the needle to the area between his upper gum and lips and move them back after inspection. In cases of extreme inspection, Houdini could manipulate the needles to be hidden beneath his tongue.
Houdini would then enter the stage and place up to 2 packets of needle and a length of thread on his tongue. He would then drink water and appear to swallow the needles and thread, place his finger and thumb to his mouth and extract the pre-threaded length of needles. At the finish, the needles stretched well across the stage. However, Houdini also had to be ready to dispose of the loose needles and thread for a post-inspection of his mouth. To do this, he would simply take a drink of water after the trick and eject the needles and thread into the glass. The weight of the needles would naturally propel them to the bottom of the glass, where they could not be immediately seen. The glass was then promptly taken away by an assistant. No special glass was needed, as the reflection of the water made it difficult to see the needles.
Houdini would also perform a variation of this trick, by using razor blades. This trick was performed in almost the same manner as the needle trick however, instead of actually placing a false set of razor blades into this mouth, Houdini would simply show the blades on a folded handkerchief that contained pre-threaded blades hidden inside one of the folds. When placing the blades onto his tongue, he would take the pre-threaded blades from the fold instead of using the actual loose blades. In this way, there was no need to dispose of the loose razor blades for a post-trick mouth inspection, as they would be hidden within the folds of the handkerchief that had been removed from the stage by an assistant.
Source: Harry Houdini - The Life of Harry Houdini