I thought there was no choice for it but to run. [Which is a totally valid life choice when you're traveling with the Doctor, trust him.]

But the Doctor stopped us, told us we mustn't believe in it, and that we had to say it didn't exist. And when we did, it stopped dead in its tracks. Turned into a picture of itself, mounted on a stand. Like one of those things you find in plays when ye need to have something there for scenery.