Sly 2:Damage

In, damage is default on contact with zap volumes which are placed around level hazards and spawned for attacks. Like, each zap volume has an assigned damage type.

Hit points
In Sly 2 each entity has a certain amount of HP. Taking damage causes you to lose some HP, and having a higher suck value adds some damage resistance.

Health pickups
Sometimes guards will drop health pickups which add 10 HP to your health when you collect them.