 getting scratched, getting something stuck in it, or some other irritation that causes the eye to weep. So tall pasture grass is a prime culprit for scratched eyes. Once the weeping begins, face flies have an attraction to the moisture, and the flies then transfer M. bovis to the irritated eye of the animal, and the pink eye sets in. The problem is that pink eye can spread rapidly throughout a herd, so once an animal has it and is not treated quickly, others are pretty sure to get it.