Ever since they started working together, there's always been an elephant in the room. (Well, train, actually, but there you go.) And it's one big elephant too, not that they're talking of literal elephants, mind you.
The thing is, the Driver is an insufferable bore and everything, but – well, you know how this sort of things go. It's plain annoying how cute and, well, attractive a man can be in spite of all his bad qualities.
And now they've accidentally exchanged a declaration of love over the intercom the metaphorical elephant has somewhat soared into the air and flown away.
