For someone who knows how to do it the technique you described is much safer than probing a baby boa. Experienced keepers don't have to actually 'pop' the hemipenes, it is a combination of judging the length and shape of the tail along with exerting just enough pressure on the tail in the right place to see how the
cloaca and the glands associated with it are everted.
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This is common practice in a wide range of Colubrids and pythons and again when done properly poses no threat to the animal.
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Hope that helps.