A: knee injury.

LOUD, STARTLING NOISES COULD LEAD TO KNEE INJURIES: To protect your knees, you may want to cover your ears. A new study finds that startling, loud noises may increase a person’s risk of knee injury. Scandinavian researchers say honking horns, sirens, and other sudden noises disrupt circuits in the brain that control muscles and ligaments that stabilize the knee, and the changes can cause people to trip and fall. In tests, participants who were startled showed significantly increased muscle stiffness compared to those who were not startled. Researchers also note that estrogen levels may affect joint looseness and neuromuscular control in women, which could have affected their findings. (Fox)