Here is a cute little song children and some childish adults use to cement promises. To make your promises seem authentic, all you have to do is hook your pinky with someone and sing the song below. However, I am not sure what ‘genman’ is:*

The YUBI KIRI Song

 

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指切りげんまん、
yubi kiri genman
“yubi kiri genman”

うそ ついたら
uso tsuitara
If (you) tell a lie…

針 千本 飲ます
hari sen bon nomasu
Drink 1000 needles

指切った。
yubi kitta
(and) cut (my) finger.

VOCAB:

指 yubi - finger
切り kiri - cut, a cut
げんまん gen man - see discussion at bottom
うそ uso - lie, a lie
うそ ついたら uso tsuitara - If tell a lie
針 hari - needle, pin
針千本 hari sen bon - 1000 needles. [the 本 is used to count needles - a thousand 千 to be precise]
飲ます nomasu - give a drink, cause to drink [same as 飲ませる]
指切った yubi kitta - finger cut

You may think this pleasant song is only sung by children of Yakuza, but you’d be wrong. Yakuza, as you probably know from the movies, are Japanese gangsters. If a member goes to prison they cut off a digit as a way to prove they are still committed to the underworld. I met a man, now a Christian, who had done this three times. Twice on one pinky and one digit on the other.

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* I looked up げんまん in the Kenkyusha J-E. It simply says it means to hook little fingers as a token of a promise. I then looked it up in the 広辞苑 (koujien) J-J. It says the same, basic thing. But it gives the kanji: 拳万 (fist + 10,000)