On a successful hit from a “blunder” weapon (including a +2 Boom Stick), this slug deals an additional 1 damage. It must be declared (turned in) before sliding the weapon token.
Weapons & ammunition made from or coated with silver do not deal extra damage to lycanthropes. (Silver Sickle is the sole exception.) However, damage from silver weapons/ammo cannot be regenerated or magically healed by lycanthropes.