I had a four foot black rat snake behind my barn the other day when I rode out, I just changed directions and went around the other way. The only time my horses have ever freaked out over a snake, it was a copperhead at dusk crawling across the path to my arena, and as I was on foot, I'm glad the horse warned me. We have a rat snake that winters in out garage every year. I never see him, but he always leaves his skin for me *shudders*. They don't bother me when they are outside or around the barn, but to know one was in my garage all winter, and I likely walked all around his hiding place, it just gives me the creeps. The last skin we found was around 6 feet and it wasn't complete.
"Keep a leg on each side and your mind in the middle"