In the episode The Sound of Drums. when Martha, Jack and The Doctor find the TARDIS, after Martha comments that the TARDIS sounds like it was sick.
The Doctor: It can't be. No no no no no. It can't be.
Martha: Doctor, what is it?
The Doctor: He's cannibalized the TARDIS.
Jack: Is this what I think it is?
The Doctor: It's a paradox machine.
It sounds like Jack had encountered a Paradox Machine before as he is about to identify it. I am wondering if it's a part of a Time Agent's Basic Training to know what a Paradox Machine is and how to identify one, or has he encountered one before? (I haven't seen a lot of Torchwood).