The Doctor is told to put down all his weapons and he places his spoon on the table. In Robot of Sherwood (2014) he uses a spoon as a weapon when fighting Robin Hood.
The four knocks the Doctor hears are the same as the sound of drums the Master heard in the third series, and a reference to the four knocks that Wilf inadvertently used to kill the Tenth Doctor in The End of Time: Part Two (2010).
Russell T. Davies jettisoned Gallifrey and the Time Lords from the series in order to free it from the baggage of its past. Its past appearances had been limited due to being part of a much larger narrative. Steven Moffat wanted to buck this trend, revisiting some established elements, while introducing new ideas.
Ken Bones returns as The General, who was last seen in The Day of the Doctor (2013). He also provided the voice emanating from Gallifrey in The Time of the Doctor (2013).
Rachel Talalay hoped that Timothy Dalton would be able to reprise the role of Rassilon from The End of Time: Part One (2009)/The End of Time: Part Two (2010). However, she soon learned that he was committed to Penny Dreadful (2014) during the required filming dates.