Rhodan and his men are brought to Naator where they are to be examined by Aras. You will remember, of course, that the plan is to get hired as recruits to get to Arkon and then somehow to fight the Empire from within.
Now, the men are disguised as Zalites. And the danger is that the Aras will discover them because they are actively looking for spies. And guess what is going to give the Terrans away? The bone structure, that is one thing, but also their higher intelligence. That’s cute. So the Ara doing a medical check will test the IQ and realize they are too smart to be Zalites.
Luckily the Mutants Corps is there to help. I remember how fascinated I was by mutants as a child. But really, it is quite boring to have them around in any case or trouble.