At the beginning of this scene, Simon Pegg’s character, Shaun, and Nick Frost’s character, Ed, are watching a news broadcast after discovering a strangely-behaving woman in their back garden.
The diegetic sounds (that the characters can hear) in this part of the scene is the two characters sitting on the couch (presumably a foley sound to amplify the effect of them sitting down), the news broadcast’s monologue, the two characters communicating, the noises of the door opening as the zombie walks into their house, and the zombie’s soft groans as it approaches – which is quieter than it should be, of which I assume was done to display the character’s lack of self awareness.
The non-diegetic sounds include the low rumbling present through the scene, and the musical sting before Ed and Shaun notice the zombie in their house.
They then attack a zombie that walks into their home with various household objects, ranging from books to pillows to an ashtray. Shaun then shuts and locks the front door after they kill the zombie.
Diegetic sounds present within this segment include the cartoonish sound effects of the objects hitting the zombie – or the window behind them – the news broadcast still running in the background, more dialogue (panting and screaming), the sound of the ashtray breaking on the zombies skull, and, while amplified for effect on the audience, the sound of the door locking.
The use of non-diegesis here is present in the tense musical score and musical sting as the zombie is killed.
More examples of non-diegesis throughout the scene is the soundtrack, with a hip-hop track briefly playing as the characters throw vinyl discs, and whoosh sound effects accompanying scene transitions.