You need to let the cow drop on or near the missing texture sprite.
How does it look like? If its the magenta/black tile, it hasn't spawned for me even once. It's the only one I'm missing :(
Yes, it's supposed to be the magenta & black checkered tile. Don't give up; you'll get it eventually!
Got it shortly after posting. It is flashing on and off instead of solid, so it's harder to notice.
