Undead is a 2003 Australian zombie-science fiction-comedy-horror film. A small town is hit by meteorites that turn its residents into ravenous zombies. Only a small group of people remain unharmed and must find a way out. They are given some help by aliens.
This clip shows a common filmmaking trope; the subversion of the climax by a moment of anticlimax, only then to switch again to climax. It is one of the oldest movie 'tricks', often used to comic effect, and it is used effectively here. Apart from the obvious humour, this short clip is actually also a very good piece of editing and the use of suspenseful music helps to build tension.