It was a cow. Didn't get much time to look, because I was headed north and she was moving west. I wasn't kidding when I said I saw hair -- she crossed about two feet in front of my front rack at a full gallop and I distinctly remember going from watching the trail to suddenly seeing the details of individual hairs just ahead of her haunches. I don't know how I missed her, but she didn't even hesitate. By the time I grabbed the brakes she was just a bunch of hooves kicking up dirt on my left side and was gone in seconds. Thankfully it was on a slower stretch of trail - a minute or so before I was doing about 40. I don't know which would've been worse -- flying over the handlebars into her, or having her stomp whatever life I had left in me afterward.