If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Why do these Zombies keep attacking the Earth? And why do you have such bad aim? Good thing the Zombies are blathering on about stupid things - you should use that, and your supreme typing skills, to target 'em!
Type those Zombies to Death!
Type Words to Kill Zombies.
Buy Upgrades to Kill Zombies Faster.