When Rez was released in Japan, it came with the Trance Vibrator -- a device you can plug into the PS2 that vibrates in rhythm with the game (and shakes violently in between the 10 sub-levels of each stage). As Jane from Game Girl Advance noticed, "it seems to have no other purpose [her emphasis] than to act as a masturbatory aid." Which is why she stuck it down her pants and wrote about it.
Mizuguchi claims the intention was for a player to put the vibrator at his or her feet or hands. One time we we were playing the US version of Rez with the Trance Vibrator in the middle of the coffee table. On the third level, it had shook itself off the table and towards some very concerned friends. Serious joke, indeed ...
See Also:
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Joystiq Interview: Tetsuya Mizuguchi
Develop: What Inspires Mizuguchi