Alright people want to know what a notail is so I'ma give a breif rundown of the race.

The thing that sets them apart from other species though is that they come from a world where evolution is really fast. As in a plant can become a completly different plant in 3 generations.
This forced them to take measures to ensure their survival, namly genetic engineering. They make notails in batches (Though normal means work, it's highly discouraged) so many have the same DNA. This is to ensure as many of them as possible get good genes.

Now as to why generally you wouldn't want to be around one. First they are good at carrying diseases. Second they subscibe to extreme Darwinism, basically meaning if they don't see a reason why a race shouldn't die they are quite willing to kill them just for existing. They are also eager to experiment on anyone/thing they can get their hands on (Just say no if they ask you).

Now I'ma just steal a bit of text:
To notails, everything is about the survival of the fittest and smartest. There is no pity for the dead and if someone a notail knows dies they will rarely be moved or saddened by it; according to the notails, that person should have been stronger, or their genes should have better. Notails create their children using a machine and a whole class, the B-reeder class, that carefully gathers and mixes genes to create the perfect batch of children in these machines. Children who are deemed "incorrect" are either disposed of right away or are sent to labs where they will be experimented on for as long as they live.

All I'm explaining next is the mask. They are very impersonal and hide their emotions. Matter of fact they consiter the mask their face and their actual face their mask. So cold, calculated, and distant really summerizes them pretty well. They arn't out to get everybody, but their are out their for themselves.