I am pretty sure it is irony and sarcasm
Answer:
Buzzards are widely known for their apperance being creepy or scary, When buzzards flock together they can be seen as one giant dark circle comparing Mr.Shiftlets thoughts or head to a group of buzzards could be taken as one dark cloud in his head or multiple eery thoughts being grouped together.
Explanation:
Im not sure if this is the answer you are looking for but this is how I would answer hope it helps!
the boys use the sticks and rocks to start the fire
