(No need for spoilers, I'm way down here at the bottom).
I thought B as well. I have a strong opinion, but I am not sure if it's any more conclusive than anyone else's.
I thought about what happens when we are searching for something specific among clutter. Or, for instance, in my messy kitchen, I can quickly and easily separate garbage from dishes. First, dishes are round and white, utensils are metallic and shiny. Anything other than that is not dishes.
If you'd sit with a pack of cards, and start dealing them in two piles based on their suit color, initially (if it's your first time), you might think a while with each one, but very soon you'll start separating them ~3-5 cards per second. It's then that you'd realize that numbers, suits, and pictures don't mean anything, and you set your vision to completely ignore those details, only focusing on it's colour.
In the image of the O.P., I think there is more visual attributes that match better between the cow and the grass. First, they are both darker while the chicken is white. They both relatively have a more similar shape than the chicken, and the rotation of that shape is also similar. Overall, they look more alike than the cow does to the chicken. Hence why 81% of the people are unconsciously choosing the grass, but explaining their decisions in all this agricultural stuff.
That's just my hypothesis. And those who chose chicken are just rebellious.