Bristles

Like normal objects, an animated broom has Hardness. This Hardness reduces any damage it takes by an amount equal to the Hardness. Once an animated broom is reduced to less than half its Hit Points, or immediately upon being damaged by a critical hit, its construct armor breaks and reducing its Armor Class to 13.

A creature hit by an animated broom's bristles must succeed at a DC 19 fortitude save or spend its next action coughing. Even if hit by multiple bristle attacks, the creature has to spend only 1 action coughing to clear the dust out. A creature who doesn't breathe is immune to this effect.