According to the pilot, prior to engine start, the co-pilot seated the passengers "to make sure they had their seat belts fastened." After startup, as the pilot started to taxi the airplane, he called for the taxi checklist, which included an emergency brake check. The hand-operated brake lever, which slid into an emergency brake position as well as a parking brake position, was "abnormally stiff," and when the pilot moved it, it slid forward enough that full hydraulic pressure was applied to the brakes, and the airplane came to a sudden stop without any pedal input. Unknown to the crew, during the brake check, a passenger had released her seat belt, and was in the process of changing seats, when the sudden stoppage occurred. She fell to the aisle, but when the co-pilot subsequently attended her, she decided to continue the trip to its destination. About 1 week later, the pilot learned that the passenger had incurred a hairline fracture to her collarbone.