Answer:
1. Sly 2. Poison 3. Quiet
Explanation:
Foxes are symbolically known as being conniving tricksters in literature, hence sly.
If the connotation is negative, as the text suggests it to be, then poison is the most suitable word, though influence could be argued.
Billy's laughter is about volume, so "still" makes the least sense, and since "quiet" is a word directly stemming from volume, it is the answer.
