It's the first test of any new Doctor Who companion – how do you react when you step inside the Tardis and realise it's bigger on the inside?
It's a scene that's played out so many times in Doctor Who history that it's really hard to make it feel fresh. Pretty much every viewer at home knows what the Tardis looks like, but it's the companion's job to make us feel like we too are seeing it for the very first time.
Well, step forward Pearl Mackie, Peter Capaldi's latest (and presumably last) companion in Doctor Who. Here, from series 10 episode one, is Bill's first look inside that famous blue box.
The new clip, from series 10 opener The Pilot, shows Bill and the Doctor attempting to hide from a slightly damp and seriously sinister 'Heather', with the Doctor suggesting they "pop into my box".
"Your box?" Bill asks incredulously. "What good is getting into a box going to do?"
"What an extraordinarily long and involved answer this is going to be," the Doctor replies to himself.
As Bill worries about the strength of the 'box's' wooden and glass doors, the Doctor steps in, presumably psyching himself up for the big reveal.
"Time And Relative Dimension In Space," he announces proudly. "Tardis for short."
"You're safe in here," he adds. "You're safe in here and you always will be."
Oh Doctor, if only that were really true...