With a lot of colubrids you can tell sex by looking at the tail. If it is long and thin it'll be male. If it's short and semi thick, then it's female. This is not 100% accurate. Not sure if probing is the same, but pretty sure popping is. Someone with better/more experience will have better advice.
Isn't it sort of the other way around?
Males have thicker tails (but longer, as you said) to store their hemipenes, whereas females taper off quickly... I believe.
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