The Doctor tosses off his leather jacket and rolls up his sleeve. Popping open one of the drawers, he pulls out a tool the size and shape of a ball-point pen. He places the tip against the inside of his elbow and clicks the plunger twice.

Then, he pulls out a slide and places a drop of the blood he collected on it, moving it under a microscope attached to a display screen. A few fiddles with the knob, and the resolution zooms in with dizzying speed to reveal an infestation of tiny spider-like creatures latching onto the surface of the blood cells and burrowing their way inside.