The real answer according to real physics:
Both bowling balls get
U T T E R L Y
O B L I T E R A T E D !
To smithereens!
Kablam! And the subsequent shrapnel goes flying off at speeds in all directions that will rip any human body (or even a spaceship) standing in the way to shreds!
Essentially this is a collision issue/problem. Bowling Ball A is going at 18,000 mph, and Bowling Ball B is at a stand still. The string connecting the two will snap, and maybe cause the two balls to spiral in instantly and collide at a differential speed of 18,000 mph.
Even if they just barely nick each other at those speeds they'll shatter into high speed projectile chaos.