I know this is a work-in-progress, but going through it frame-by-frame (its so short, I'm justified!) I noticed that the falling walker doesn't move for the first frame. I KNOW you're going to fix it, but I can't be too safe by not saying anything.
It's impossible to see in the full motion, I'm just having a great time flipping back and forth as everything moves but the walker defies all logic and stays perfectly still!