Most of the people says that the Tardis is bigger on the inside, and that’s always all the time. But… that not happen every time. The sequence is taken from the Snowmen, the Christmas Special episode from 2012, when the Doctor takes Clara inside the Tardis.
It’s the first time we all see the new look, even if it was announced some time ago.
“It’s called the TARDIS. It can travel anywhere in time and space. And it’s mine!”
“But this… Look at this…”
“Go on, say it. Most people do…”
“It’s smaller on the outside.”
“This is the day, this is the day, this is the day everything begins!”