A video showing Roger Federer knocking a bottle off a man's head with an eerily accurate tennis serve has gone viral online, and left people around the world wondering whether the clip involves any digital sleight-of-hand. In the midst a photoshoot for sponsor Gillette, Federer is shown twice using a well-executed serve to hit a glass bottle off a nervous production crew member's head. Pundits have called foul, speculating the video was faked by Gillette as part of a guerrilla marketing campaign. The personal care company added to the intrigue by refusing to confirm or deny whether the footage had been digitally altered. "If anyone could do it, it'd be" Federer, says Ron Hogan at PopFi. But "if anyone might fake it for a viral ad, it's Gillette" — after all, they're trying to compete with the Old Spice Guy. But Federer's own website has posted the trickshot, says Henry Blodget at Business Insider. If it really was a fake, would Federer "sacrifice his own cred for the cause"? Watch Federer's "William Tell" video: