Would a werewolf hit with non-magical damage leave a blood trail?

Question

Say, for example, a werewolf triggers a spike trap and fails the DEX save to avoid the spikes. However, they're just iron spikes, not silvered or magical. Would this cause them to shed blood, since they take no damage, or would they just be pinned in place until the trap reset?

Answer 1

If the werewolf takes no damage, there probably isn't any blood. They'll suffer any non-damage effects.

Well, firstly, from a mechanical standpoint, if the werewolf gets hit with a spike trap and fails their save, they won't take any damage, but they should still suffer any non-damage effects as long as they're not contingent on taking damage. If the trap pins anyone who gets hit by it in place, then they'll get pinned in place. If it reduces movement speed until the damage is healed like caltrops, then no movement speed reduction occurs because there's no damage to be healed. If the spikes are coated by an injury poison, no poison damage would be inflicted, since no piercing or slashing damage was taken, but if they were coated with a contact poison, the werewolf would be affected by the poison since it made contact with them.

I would also say that it's unlikely that they'd leave a blood trail. The sidebar "Describing the Effects of Damage" on p. 197 of the Player's Handbook says the following:

When your current hit point total is half or more of your hit point maximum, you typically show no signs of injury. When you drop below half your hit point maximum, you show signs of wear, such as cuts and bruises. An attack that reduces you to 0 hit points strikes you directly, leaving a bleeding injury or other trauma, or it simply knocks you unconscious.

As such, I'd say that creatures in general would likely only leave a blood trail that could potentially be tracked when reduced to half or less of their maximum HP. Since the trap does no damage to the werewolf, it's unlikely that it would contribute to this.

Answer 2

It's up to the DM's interpretation

You are still hit by attacks to which you are immune. A hit that does no damage can still harm the target, such as by spreading lycanthropy to them.

There's no specific rule that says when a character does and does not bleed as a result of an attack. So a DM could rule either way: 1) that the werewolf bleeds without being harmed enough to take damage (perhaps the equivalent of a scrape that bleeds slightly without doing any real harm), or 2) that because they are entirely immune to the damage, they are not wounded at and thus do not bleed.

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Personally, I would rule that because they are entirely immune to the damage, they don't bleed, at least not enough to leave a trail. But that part is just my opinion.