The Wounding Modifiers and Injury rules assume a human, animal, or other ordinary living being. Machines, corporeal undead, swarms, and other unusual entities are much less vulnerable to certain damage types:
Unliving: Machines and anyone with Injury Tolerance (Unliving) (p. 60), such as most corporeal undead, are less vulnerable to impaling and piercing damage. This gives impaling and huge piercing a wounding modifier of x1; large piercing, x1/2; piercing, x1/3; and small piercing, x1/5.
Homogenous: Things that lack vulnerable internal parts or mechanisms – such as uniformly solid or hollow objects (e.g., melee weapons, shields, and furniture), unpowered vehicles, trees, and walls – are even less vulnerable! This includes animated statues, blobs, and anything else with Injury Tolerance (Homogenous). Impaling and huge piercing have a wounding modifier of x1/2; large piercing, x1/3; piercing, x1/5; and small piercing, x1/10.
Diffuse: A target with Injury Tolerance (Diffuse) is even harder to damage! This includes swarms, air elementals, nets, etc. Impaling and piercing attacks (of any size) never do more than 1 HP of injury, regardless of penetrating damage! Other attacks can never do more than 2 HP of injury. Exception: Area-effect, cone, and explosion attacks cause normal injury.
Example: Edmund Zhang empties his 9mm machine pistol (2d+2 pi damage) at an approaching zombie. He hits three times. After subtracting the zombie’s DR 1, he scores 8 points of penetrating damage with the first bullet, 7 with the second, and 10 with the third. The zombie has Injury Tolerance (Unliving), so the usual ¥1 wounding modifier for piercing damage drops to ¥1/3. Rounding down, the three bullets inflict 2 HP, 2 HP, and 3 HP of injury. The zombie had 24 HP, so it has 17 HP left. Undaunted, it shambles forward. Edmund should have brought an axe or a flamethrower!