Not much to ponder for a viewer seeing a film for the first time, but think about how the film unfolds after that. Shaun and Ed kill a zombie named Mary. They then go to Shaun’s stepfather’s place to find out he’s been bitten. Off to rescue Liz (Shaun's love interest) at her flat and then the group pretends to be zombies and infiltrate The Winchester where they fend off zombies with a rifle.
The entire film is described in one line. Brilliant.