When two girls use a double sided dildo simultaneously then make a wish before pulling out. The girl that retains the dildo in her snatch will have her wish granted.
Girl1: Wanna wishbone (lesbian wishbone)? I'll make all your wishes come true.
Girl2: You betcha.
Girl1: You got some pussy muscles on you girl, what was your wish.
Girl2: *giggles* If I tell you, it won't come true!