"That's a fine sheep, isn't it ?" said Miss Laura, pointing to one with the blackest face, and the blackest legs, and largest body of those near us.
"Yes; that's old Jessica.

Do you notice how she's holding her head close to the ground ?" "Yes; is there any reason for it ?" "There is.

She's afraid of the grub fly.

You often see sheep holding their noses in that way in the summer time.

It is to prevent the fly from going into their nostrils, and depositing an egg, which will turn into a grub and annoy and worry them.