Guys, we were so wrong.
We've been misinterpreting horse plinko all along.
It's a three-dimensional scene, but depicted without depth perspective. The round things are actually hay bales in a field leading off into the distance and the horse is weaving between them as it moves towards us, with the fire in the foreground.
Thank you, 'sperm flagellar control' side of 'horse plinko lore' tumblr
I cannot, cannot stress enough how difficult this sort of interaction is to find outside Tumblr.