The video, posted on YouTube, contained staples of underground fighters’ messages in the Internet age: 11 men dressed in black, each with his face hidden behind ski masks or cloth, posing with what appeared to be modified MP-5 submachine guns, a weapon often in service with counterterrorism teams. …

According to an analysis by a curator at a British arms museum, the 11 men were each holding a TD-2007, a Chinese-made toy replica of the MP-5 submachine gun, marketed as appropriate for children above the age of 5. To each, the men had affixed an extension — perhaps a painted dowel or a section of pipe — masquerading as a long barrel. …

Who made the video is not known; it was apparently posted by an opposition sympathizer this spring, part of the daily circulation from Syria of videos showing the suffering or activities of Mr. Assad’s opponents. The deception unraveled once Mr. Ferguson watched the video on Wednesday and realized that each man held his weapon with his left hand in a way that concealed where the fake barrel met the toy; then he noticed other parts that were out of proportion. A Web search found the match.