Viruses?
Overall, the medical examination took way longer than Nial expected. They took a look at every nook and cranny of his body to make sure that he was not infested by some sort of highly contagious virus that was deadly to the Demihumans.
Apparently, there had been problems with something like that in the past. Some 'aliens' brought highly contagious viruses to their territory, not knowing that they had something like that attached to them, in the first place. The aliens were unaffected by these viruses while the Demihuman died like flies that were flying into the blazing flames of a campfire.
Nial's body was not the only thing that had to be tested, but his mind was as well. While the examination of his body took a total of three days in which he was isolated, he learned the Demihumans' language both the written language and the spoken language. He knew that the questions they would ask would be easier to answer knowing their language.