50% possible het means that you have a 50% chance of proving it out. (The snake has a 50% chance of carrying the gene.)

66% possible het means that you have a 66% chance of proving it out. (The snake has a 66% chance of carrying the gene.)

So, I would imagine that people are successful proving out 50% and 66% possible hets about 50% and 66% of the time, respectively. I know that there are quite a few folks on this board who have done so ... I have a whole little army of possible hets that I'm hoping to try and prove out in the coming years. (I'm gonna be real stoked if even 50% of them prove!)

In theory, you can increase your chances of proving one out by looking for possible hets with "marker traits," alterations in the pattern of the animal that suggest the influence of a heterozygous recessive gene behind the scenes. This is especially well-known in het pieds, in which the pied gene seems to "break through" on occasion even if only heterozygous. (Not producing a pied pattern, but "funking up" the pattern a bit.)