JO: A mind probe?

DOCTOR: Oh, you don't want to worry about those things, Jo. As long as you tell them the truth, they can't do you any harm.

JO: They can't?

DOCTOR: No, of course not. Well, they're only sort of computers with a few extra knobs on. And you know how stupid computers can be, don't you? Now come and sit down, stop worrying. Come on. Sit down. Did I ever tell you the story about how I was once captured by the Medusoids?

JO: What are they?

DOCTOR: Medusoids? How can I describe them to you? Well, they're a sort of hairy jellyfish with claws, teeth and a leg.

JO: Erk!

DOCTOR: Anyway, they put me under one of these mind probes things, you see, and tried to get me to tell them where I was going. So, I said I was on my way to meet a giant rabbit, a pink elephant and a purple horse with yellow spots.

JO: What happened?

DOCTOR: Well, the poor old machine just couldn't believe it, had a nervous breakdown.

JO: And then what happened?

DOCTOR: Well, they put me under another one of these mind probe things and the same thing happened.

JO: But you weren't telling the truth. I mean, you weren't really going to meet a giant rabbit, a pink elephant and a, what was it?

DOCTOR: A purple horse with yellow spots. Yes, I was. You see, they were all delegates for the third Intergalactic Peace Conference.

JO: How did you get away from these things?

DOCTOR: Well they had to turn me loose eventually.

JO: Why?

DOCTOR: They ran out of mind probes.