If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
R - reload.
You are now living within a zombie infestation and the world is a pitiful state. You need to look after yourself and you alone but you welcome the action and the crazieness it is the only human emotion left to you and makes you feel alive again! So go and take more zombies out in a fun filled shooting gore fest night!