Because the catrating knife went so deep when it was cutting the sac open that it went completly through the sac into the testicle and made a cut the cut you referred to in the testicle at the same time.
Unnecessray pain for the bull since there are ********** knives available that have a small curve or hook on the end of the blade that help prevent cutting into the testicles while assuring the sac is cut completely open .