It's used to attack the pressure points, and disturb the breath control, after which the opponent is virtually helpless.
8 seconds sound clip from the The Invincible Armour movie soundboard.
You can hear this line at 00:54:12 in the DVD version of the movie.
Quote context
[...]
- Right. I trust you. Three days.
- The Iron Finger was designed to combat Iron Armor.
- The whole body strength is concentrated in the fingertips.
- Right!
- Wake me early in the morning.
- A great irony. Boiled beans with bean stalks? I see.
[...]