>>11389147
The only obvious thing that comes to mind is that Scarrans sometime rape Sebacians, so they are definitely turned on by the human form. Also Ben Browder's wife portrayed the Scarran War Minister, so he has played with Scarran pussy IRL (and I'm sure she had fun torturing him in that brain probing device).
Since they are very reptilian in appearance I would guess they have a cloaca. Everything would be deeply hidden inside the Scarran body and they would be really embarrassed to show it, although we would never notice because their blushing is not visible on our spectrum.
If you got to know a Scarran really well they would invisibly blush while guiding your hand toward their cloacal opening (which contains their genitals). They would subtly imply that you need to put you hand inside, until you do it and realise why they were so insistent to begin with.