Learning how to tell the sex of a salt water crocodile, it requires putting your hand into the animals cloaca and depending on what you feel - or don't feel, you can tell the difference between a male and a female. Three metres and over will always be male but under 3 metres could be either so we had to know which were which so we could place them in the correct ponds.
That was 20 years ago in Broome.

