Aim the catapult to launch the zombie into the coffin. The smart obstacles will make your task harder. Select the shot size which would give you the best trajectory for the zombie's flight. Use the catapult wisely. Fill the sky with flying zombies!
Press and hold the left mouse button on the blue square. Let go when the shot's size gets as big as you want it. If you need more zombies for a new try, press the button to the left of the blue field.