Spiders.
I had a freak-out moment today. I was carrying my groceries inside and walked into a spiderweb without realizing it. It brushed against my arm and my initial response (which was pure instinct) was to flail my arm like a crazy person. After a second or two of that I snapped out of it and realized it was just a spiderweb. After that incident I started thinking about how my response to that situation was completely primal. I must have ancient genetic coding that keeps me from walking into giant, man-eating spider webs. A lot of good it does me now.