What does that mean? Sheep are hellish, difficult to work with, and generally bloody annoying? Or something else? "Sheep are hell" makes a lot more sense than "sheep are **A** hell".
Uhhh, however you want to interpret it :) And an "A" doesn't change much either—feel free to get creative with your interpretation ;)
I kinda already had an idea going in and it fit close enough if I interpreted it as like "the sheep are in hell" 💀