JOEL: Also I might have invented the sandwich.

DOCTOR: No, you can't have.

JOEL: Why?

DOCTOR: Because I invented the sandwich.

DOCTOR: You're thinking of time as a strict progression of cause and effect, but actually from a non-linear, non-subjective viewpoint, it's more like...

GABBY: Like a...

DOCTOR: I don't know. I'll think of a good end to that sentence one day.