Testing for blood..
It happened in Screamers and in this film, as well as many other films, like The Thing.
So the issue in the Screamers franchise is in both films a character gets their palm slashed open. Not only is it going to hurt, a lot, but it's also going to cripple that hand which is a pretty stupid thing to do especially in the scenario they are in, where having good reflexes and dexterity are vital for dealing with, Screamers.