The next time some pervert pinches your behind on the Tokyo subway, ask them if they've played the new butt-poking arcade game Boong-Ga Boong-Ga that is sweeping Japan.

In Boong-Ga Boong-Ga, known in English as "Spank 'em!" the player jabs a plastic finger into a jeans-covered bottom, which juts from the machine as if a person's head and torso were stuck inside. Developed by a Korean company, Taff System, the game was received enthusiastically at the Tokyo Game Show last year. Taff System recently signed a deal to distribute 200 Boong-Ga Boong-Ga machines in arcades all around Japan. Boong-Ga Boong-Ga leaves little to the imagination. Players can choose between eight tushy targets, including "ex-girlfriend," "ex-boyfriend," "golddigger," and "prostitute." Other characters include "mother-in-law," "child molester" and "con man." The player is not expected to spank the protruding bottom exactly, but to poke it enthusiastically with the attached plastic finger. On the screen, the character's face grimaces and screams with each finger thrust. The harder a player pokes the rear end, the higher his or her virility is rated. At the end of the game, the machine prints out a card explaining the player's "sexual behavior." Taff promotes Boong-Ga Boong-Ga as a safe outlet for players' pent-up frustrations. Academics and politicians have often blamed video games, rock music and TV for promoting everything from obesity to mass murder. But although female straphangers in the Tokyo subway system are often groped and pinched, it may be a stretch to reproach Boong-Ga Boong-Ga and similar games for causing such sexual assaults.