In this method, a metal probe is slipped through the vent to check for the presence of a hemipenis, the male copulatory organ. Every male has two hemipenes in the base of the tail. A simple visual examination of the tail's length and thickness. The hemipenes make the tails of males longer and thicker than the tails of females of the same size. When looked at from the side, male tails are generally half as thick at the middle as at the base.
Female tails are usually half as thick a quarter of the tail's length from the base.
While learning, look at adult snakes of known sex before trying it on juveniles and adults of unknown sex. Male boa constrictors and pythons have spurs on either side of the vent that are longer than those of the females. In general, breeding snakes requires closely copying their natural conditions. Although captive breeding should be encouraged, it requires more dedication than simply keeping a few snakes. Records of origin, feeding, shedding, and breeding should be kept.