Analysis of information sources in references of the Wikipedia article "Flatulence" in English language version.
Trevor Blank [...] found Pennsylvania boys playing "Safety," a farting game, the same as Blank had as a kid in Maryland, and the same game John Bourke documented in the 1890s, when it was called "Touch Wood." Basically, a boy who farts must say "Safety" or touch wood before his friends say another key phrase. If not, they're allowed to punch him. (It usually is boys who make farting a game or a weapon.)