The familiar knocking of knuckles spreads only one-twentieth the amount of bacteria that a handshake does, researchers report. [...] fist bumps — popularized by Barack Obama and others — seem to be the wisest greeting, especially during cold and flu season, said researcher David Whitworth of Aberystwyth University in Wales. [...] the researchers realized that while a lot of research focused on hands getting germy from touching doorknobs and other surfaces, only a few studies had looked at handshakes. [...] there are alternatives to handshakes. The researchers did practice runs with paint to measure how much surface area each form of greeting involved. Online: