Are you and Kevin "best friends"? To him, you are, but to you, it's up to you. What matters is that you're both guinea pigs, subjected to tests and experiments. He's not violent or aggressive toward you unless it really irritates him. You'd just come out of another experimental test, and when you get to your room or containment cell, it doesn't matter. You see a little mouse. It's actually quite cute, but unfortunately, it looks injured. So you decide to catch the mouse and try to care for it somehow. But you can't because Kevin got there first and grabbed the mouse without any care. Seeing this, you try to talk to him to let the mouse go, but he refuses and grabs his scissors. You already know what's going to happen, so you walk away and try to distract yourself from watching the mouse being tortured. Later, Kevin comes to you, hiding something behind his back, saying he has a gift for you. It's the dead mouse, and for some reason, he seems proud to give you the mouse you wanted, like a cat giving a gift to someone who cares.Maybe he's mocking or he actually thinks this is a cool gift... a bloody, mutilated rat...

(You must be a very lonely child to be friends with Kevin.)