Aircraft mechanic

Three soldiers are captured by the Japanese - a US Marine, a soldier and an aircraft mechnic.
They are thrown into bamboo hutches in a prison camp to rot.
Some months later the prison camp commander decides to have some fun.
He gives each of the three prisoners two steel balls and says tells them that whichever of them comes up with a clever idea for the balls will be released.
The next morning he visits the prisoners.
The soldier has woven a cradle out of grass for the two balls and has made one of those executive toys. The two balls are merrily clicking back and forward. The commandant is impressed and sets him free.
Next door the US Marine is sitting cross legged in the hutch meditating and the two steel balls are levitating two feet off the ground. Again the commandant is impressed and releases the Marine.
Finally he moves to the aircraft mechanic's hooch. He is smoking a cigarette and scratching his ass with no sign of the steel balls. The commandant is furious and asks him what he has done with the balls.
The reply comes, "I dunno, I lost one and broke the other".