The Hero will succeed if all the buttons that appear are pressed quickly without missing any. The zombie will then be killed and normal gameplay will resume. While this is happening, other zombies can still move, but will not attack until the sequence is over.
If the sequence fails, the Hero will push away the zombie, leaving it unharmed and will take damage. The now freed Zombie will be capable of inflicting damage right after. Manually decapitating Zombies appears to work on most types of Zombies, including the SWAT Zombie. It treats all zombies the same, with the exception of the Hulk Zombie and the like.