Doctor Who Series 10: 12 Easter Eggs & References You Might've Missed In "Knock Knock'

When on the run from the woodlice, Bill attempts to find the trick book on a bookshelf that will activate the secret door to the house's forbidden tower. As she does so, she namedrops where she gets the idea from: "Indiana Jones... Come on!"

While the bookcase concealing a secret passageway is a classic trope of adventure fiction, it doesn't exactly feature in any Indiana Jones film to date.

What Bill - and writer Mike Bartlett - is probably harking back to is an incident in Indiana Jones and the Last Crusade. In that movie, Indy and his pops Henry Jones Sr use a revolving fireplace. Something that was previously alluded to in Doctor Who in 2006's The Girl in the Fireplace.