expression
pinky swear rhyme; cross my heart and hope to die, stick a needle in my eye
A children's rhyme recited while making a pinky swear (指切り). The literal meaning is a threat: if you lie, you must drink a thousand needles. Used playfully to seal a promise.
See also: 指切り
「指切りげんまん、嘘ついたら針千本飲ます！」と子供たちが約束を交わした。
The children made a promise, reciting, "Cross my heart and hope to die, stick a needle in my eye!"
別れ際、二人は「指切りげんまん、嘘ついたら針千本飲ます」と小指を絡めた。
As they parted, the two linked pinkies and recited the full pinky-swear rhyme.
指切り is the act of linking pinkies to make a promise; the full phrase 指切りげんまん... is the rhyme often recited during the gesture.
The phrase is a traditional Japanese children's rhyme. げんまん is said to derive from 拳万 (a fist and ten thousand), possibly implying a severe punishment. The threat of drinking a thousand needles is a hyperbolic penalty for breaking a pinky swear.