At first Martha’s convinced it has to be some kind of delusion, or optical illusion. Nowhere can be bigger on the inside than on the outside! It makes no logical sense; it has to be a trick of some kind. Maybe it’s done with mirrors.
She doesn’t know why the TARDIS should be so hard to get her head around. The hospital wound up on the moon not long ago, and if she can accept that as real then surely the Doctor’s spaceship shouldn’t be too hard to believe. And yet it is.
When did her life stop making sense?