That was one freaky episode. They are in this shuttle, with windows shut because of radiation, where they are going to a waterfall made of sapphire when this weird creature attacks. Basically, it took over the mind of a person, repeating what people said, creeping in inside people’s head, eventually ending in paranoia. It was quiet different from other episodes. It was kind of like a psycho thriller, with one of the very few times in which the Doctor is helpless. Anyways, a must see.
Cool, I found a cool web page with animations about biology. The link: http://www.hybridmedicalanimation.com/demoReel.html Some choices are artistic, but it will make you appreciate the beauty of science (which is one of the goals of this blog, whether you like it or not)
Anyways, credits to pharyngula