Never mess with an angry human wearing steel-toe boots.
Normal shoes actually.The story told about recent happening of someone who step on and destroy yukkuri's mouth like that. The narrator saw several of such yukkuri afterward, only able to make muffled sound.
He then remember an interview with yukkuri researcher commenting about how just destroying their mouth is enough. They can't scrap the trash anymore, they can't sing anymore and can't make noises anymore.
Last, a Reimu came to him demanding to be made a pet yukkuri, but he destroyed that Reimu's mouth too.
Droopy-mouth yukkuri isn't adorable at all! >:I
Lol this anko, Now I can picture the campaign of awareness:
"Help the city with it's Stray Yu Problem! Kick them in the Face! No Mouth = No Yu!"