Doctor Who Series 10: 11 Easter Eggs & References In 'Oxygen'
8. Distress Calls
The TARDIS receives a distress call in this episode and it turns out that the Doctor loves them, and even considers them his "theme tune."
The Doctor responding to a distress call feels like one of those tropes of Doctor Who that has been used many, many times. Actually, however, it is fairly rare. The first instance, for example, occurred twelve years into the show's run in 1975's Planet of Evil.
Other instances of it include Horror of Fang Rock, The Armageddon Factor, Planet of Fire and The Doctor's Wife.