ゆびきりげんまん、うそついたらはりせんぼんのます

指  切りげんまん、嘘ついたら針  千  本  飲ます

expressions (phrases, clauses, etc.)

cross my heart and hope to die, stick a needle in my eye, pinky promise pledge: if you're lying, I'll make you drink a thousand needles
said by children when making a pinky swear
idiomatic expression