Why did "Thundersnow" refuse to run in the Derby?

If you saw this year's Kentucky Derby, you might note that one of the horses wanted absolutely nothing to do with racing.

Why?

While I'm not familiar with the horse, I could tell immediately why the horse refused to compete and tried to toss his jockey. And no, he was not hurt.

The track was basically a swimming pool - it was deep mud - and some horses just won't run on mud. He slipped a bit coming out of the stall and apparently decided that no, he was not risking it. His jockey made the sensible decision not to push the matter.

The ultimate reason: All of the horse's previous dirt track experience was in the UAE. Where, ya know, it doesn't rain very often.

Here's the official video so you can see a horse saying NO with all its might for yourself.