PLAY ON PHOSPHORUS! https://phosphorus.github.io/app.html?id=131044008&turbo=false&full-screen=true Move your mouse up and down to make the flashes move up and down. Switch backdrop with space.
Credit to @neal867 for technique. It helped me to animate this better! Credit to @lego24 for his Reverse Flash remix. I upgraded it and imported it into this project to give another example! Credit to @griffpatch for his original scratch cat walk frame animation!
