The flashbacks here establish the first time that Susan meets Steve, and the first time she and Sally encounter Patrick.
The first time we see inside Sally's flat.
The painting that Sally looks at, and says that she hates, in the cloakroom is "The Scream" by Edvard Munch. Writer Stephan Moffat is said to have taken this painting as inspiration for the Silence in his writing on Doctor Who.
Sally calls Patrick 'Spider-Man' throughout this episode, when she's in Blockbuster in the final scene the Spider-Man game and video are clearly on display.
A big plot point involves a woman asking a man to come over and dispose of a spider. Kate Isitt (Sally) previously appeared in Black Canary (1998) in which a woman asked a man to come over and dispose of a cockroach.