A dangerous game there, bucko.
Here are the official rules:
Pull My Finger requires 2 players.
When Player 1 (preferably an adult) detects a potentially audible gastric lapse descending into the firing chamber, he must extend his left or right index finger directly at Player 2 (preferably a person under the age of 5) and must say the phrase "Pull My Finger".
Player 2 must firmly grasp the extended digit and tug once, firmly.
When Player 1 detects the tug on the digit he must release the gastric lapse in the most audibly disgusting manner possible.
(WARNING: Player 1 must not attempt to force the gastric lapse from the firing chamber. There are dangers associated with this practice which will ruin the game as well as Player 1's linens.)