River carries a sonic trowel. While this reflects her profession as an archaeologist, it is also something of a family tradition: her grandfather, Brian Williams (the father of companion Rory Williams), always carried a trowel.
This was originally meant to be the end of Steven Moffat's tenure as showrunner. Chris Chibnall was expected to take over, but when his appointment would be delayed due to his commitment to the third season of Broadchurch (2013), Moffat stayed on for one more year.
The Doctor says that River was once married to Stephen Fry, who had previously voiced the Minister of Chance in Doctor Who: Death Comes to Time (2001) and would later play C in Spyfall: Part One (2020).
This is the first episode where both the Doctor and his companion are played by people over the age of 50.
Among the items River Song removes from her bag to make room for the head is a red fez.