When I press A for Angry Eyebrow, the normal eyebrow is still there. What step did I leave out?
I found the answer to my own question. I watched a tutorial on triggers and found out why I was seeing two sets of eyebrows at once. In the rigging window when I double clicked on angry eyebrows, I had to scroll down on the properties panel to see where the trigger settings were and check the "hide others in group". Now it is working.
Glad you figured it out! There's a new, easier to understand triggers system (and dedicated panel) in the next update, so hopefully it will be even easier soon.