Your description of your feet running in place is a funny mental picture. I think I do the same thing, or else just freeze in place and can't move at all.
There are no poisonous snakes in RMNP, but there are definitely an abundance of snakes in that portion of the park. I once saw two within minutes of each other on the Fern Lake trail near the trailhead, and it seems like a lot of people have seen them in the Fern Lake TH and Cub Lake vicinity.
I also saw one once right on the riverwalk in EP, and I screamed bloody murder. People were jumping up and looking out the windows of the shops and restaurants. Embarrassed my son to death.
Here's proof: