What was the purpose of the ropes on the waterbeds in chapter 17 of percy jackson

The ropes are intended to hold and stretch to death the individual who lay down on the waterbed.

Explanation:

The question presented above refers to "The Lightning Thief" written by Rick Riordan, where we are introduced to Percy Jackson a boy who is Poseidon's son with a human, becoming a demigod. Percy is accused of stealing one of Zeus' lightning bolts and needs, along with his friends, to find a way to prove his innocence.

While reading this story, we are introduced to a character named Crusty, who owns a waterbed shop. Crusty, in fact, is a cruel and dishonest sorcerer, who tricks customers into trying out the waterbeds. When customers get down on waterbeds, Crusty shouts the word "Ergo," which causes huge ropes to come out from under the waterbed, trap customers and stretch them to death.

the audience knows that nora is intentionally failing to dance correctly, but helmer doesnt

the following key ideas correctly express the key sentence.

restate key idea: most people can learn to swim in ten short lessons.

restate key idea: the majority of water-accident victims require mouth-to-mouth breathing.

restate key idea: an empty, tightly closed gallon jug will support a tired swimmer.  

restate key idea: first aid is to prevent accidents as well as assist in rescue.

explanation: the key idea needs to have the same topic as the key sentence (drowning and safety).