Answer:
https://dit69.pro/duoc-2-em-gai-dam-lam-tinh-suong-vai-chim/
Grover let Percy's mom "die" and was supposed to give Percy a safe passage to Camp Half Blood.
It allows him to hear the war drum that forces him to kill. The acute silence makes the narrator so uncomfortable, he must make the old man scream. The narrator thinks that only killing the old man will make all of the surrounding noises disappear
Among the fairy tales, the story that suggest an indirect cause is Jack who killed the giant because he sold the cow for magic beans. Before Jack killed the giant, the magic beans that he trade with his cow grew into an enormous beanstalk.