It just popped into my head.
The boggart was a scrawny, slimy thing, and even a year ago it would have fled at the sight of a child. Now, it brazenly fed on the corpse in the alley, its body shivering in excitement as it gnawed. Not even the presence of a warrior with a knife in his hand advancing on the filthy beast seemed to disturb it.
Its outraged howl when a harsh hand ripped it from its meal turned into a shriek of pain as it was driven face-first into the ancient, rotting brick of the alleyway. The warrior’s companion winced at the sound of bones snapping from the impact, but said nothing as his friend’s blade buried itself in the boggart’s side.
“Mind its bile,” he did say as the warrior dexterously avoided both the foul spew from the beast’s guts, and the slightly-barbed tail trying to at least make one last strike in death. “Tis said they were bred to sicken those that slew them.”
“Not my first boggart, Nat,” the warrior grunted. “Won’t be my last, neither.”