Elder sister

Your elder sister is always in her room. She only comes out for food. And she also doesn’t let anyone inside. It is going to be difficult for you to get a sample of her DNA. You head towards her room and knock. “Who is it? What happened?” she asks without opening the door. “It’s me” you reply. You understand by her footsteps that she got up and is coming towards the door. She comes out and stands on the door in a way that no can see anything inside and asks “What?”

You don’t know what to say. But you gotta think of something quick.