You must shoot the zombies attacking scientists. Rescuing them often provides extra lives or health items, but shooting a scientist directly will cost you one life.
You start with a limited number of lives (maximum of 5). Taking damage from an enemy or a projectile costs one life. House Of Dead Game Full Version
If you successfully rescue every scientist in the first three stages, you will unlock a secret bonus room in Stage 4 containing gold coins and golden frogs for massive points. You must shoot the zombies attacking scientists
