If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
You have 60 seconds to bite as much people as possible. People you bite will turn into zombies and bite other people and soon you'll have a zombie army fighting for you. Be careful and escape from the police... or turn them into zombies as well. Collect power up's and get into Bloodrun- mode to kill even faster.