Now** that image **is perfectly clear! Evidently Shakespeare didn’t have any sheep handy to work with.
He probably worked with sheep in his native Warwickshire, but found it hard to get his hands on a sheep in the big city.
On the other hand, his wife was back home in Stratford raising the children, so he must have filled the empty hours in London with something apart from writing poems and plays. At least, the movie Shakespeare in Love suggests as much.
You don’t know your Shakespeare. In that same speech Iago says
“An Old Black Ram is Tupping your White Ewe”
Apropos of nothing, I played Roderigo in Othello once, which means I got to stand on stage a lot and be impressed by how much better Iago’s dialogue was than mine.