JO: Doctor, what did you see?

DOCTOR: Fire.

JO: But why should you?

DOCTOR: Well, some time ago, Jo, I witnessed a terrible catastrophe. A whole world just, just disappeared in flames. Well, this machine picked that memory out of my mind and used it to attack me.

JO: This fire you saw, it wasn't real.

DOCTOR: Neither was the water, nor the rats, yet Linwood is dead and so is Professor Kettering. We believe what our minds tell us to, Jo.