touched on in this thread. Bill's response was outstanding and spelled the process out very well. Although all of his information was important, one of the points he made that can not be emphasized enough is that you should never hold a boid behind the head for any reason. This is especially true for the larger species, even when young. With the strength they have in their neck muscles, if they struggle (and they usually will), it is extremely easy for them to cause permanent damage to their neck vertebrae when held in this manner. Not to mention the fact that you will produce an extremely head shy, and nervous snake very quickly. I have worked with large constrictors for over 30 years and have never had to resort to restraining one in this manner.
The other important point was made by Reticguy. Genetics does play an extremely large role in the temperament of any snake. This has been proven true time and time again, and is a definite fact. Docile parents will typically produce docile young in the majority of cases. Although many highstrung snakes can be calmed down significantly by acclimating them to handling, there will always be a few that will never become adjusted to handling, no matter how careful you are. Fortunately, these are in the minority, especially when dealing with captive bred snakes.
Kelly