Here's how it worked:
* Distraction: The killer, Dr. Roylott, used the bell rope to create a loud noise that would distract his stepdaughter, Helen Stoner, from any other sounds.
* Communication: The rope was connected to a mechanism in the room next door, which allowed Dr. Roylott to send a signal to his deadly pet, the speckled band, to enter Helen's room. This was the crucial element of the plan, as the bell ringing signaled the snake's arrival.
The bell rope itself was not inherently dangerous, but it played a crucial role in the killer's elaborate plan. It served as a tool to both confuse and control, ultimately leading to the tragic death of Helen Stoner.