Another working bike of Mexico. These knife-sharpening bikes are a fairly common sight.
The rear rack of the bike has room for a tool box and the rotating grinding wheels. Finding a good spot on the sidewalk to set up, the rider flips the kickstand down, then lowers the drive wheel of the grinder down onto the rear wheel of the bike. Sitting on a makeshift foam pad (not the most comfortable looking seat), he pedals the fixed gear backwards to start the grinding wheels spinning, and your knife is sharpened in a jiffy.