Answer:
Patients continued to feel pain as long as they believed it existed
Step-by-step explanation:
According to the given excerpt, Franklin watches in amazement as the patients respond to Charles but when he tried it for himself, he felt nothing, so he decided to blindfold the patients and see if Charles would still have the same effect on them.
Therefore, the detail that best completes the summary is that patients continued to feel pain as long as they believed it existed