The friend

"Mom!" One of the girls screamed at her mother's twitching body, collapsing on the ground. Her mother's eyes are dilated. The other couples rushed in to help. 

"Mom! What's wrong with my mom?" The girl went hysterical. She tightly clasped her sister's elbow as the other hugged her closer to her chest.

The two brothers also went in to see. But before they could step in, the crisp sound of bone breaking erupted into the still night. The sound was followed by another. By the time the snapping of bones stopped, everyone present screamed in horror. 

They saw the mother of the girl lying with her arms and legs twisted at an unnatural angle. They began to hysterically jump back, anxious about their surroundings. All of them could swear no one touched or broke her bones. It was logically impossible for the woman herself to break her bone by twisting it that way.