Phosphorus Candle was a lighting spell, with no inherent offensive power, but when it exploded directly in front of one's face, it could blind them significantly — especially fatal for creatures like rabbits.
Rabbits are different from humans; they have an almost 360° field of vision, meaning they can see everything around their entire body. Compared to the human field of view of 188°, they see much more, and consequently, are more sensitive to the stimulus of bright light.
Additionally, rabbits are crepuscular, their vision is strongest at dawn, dusk, or—as in the current situation—under the bright moonlight of the deep night.
Under such circumstances, when the spell "Phosphorus Candle" exploded right in front of its face, for the rabbit it was akin to being hit by a flashbang at maximum eye opening, from all directions.
The rabbit screamed as it hit the ground, and Richard, without a hint of politeness, swung his dagger down to stab.
