the GIF: at first I could not remember where and when I made it - was on-line. I liked it so much that I am using it as a sort of final point in my posts.
There are a couple of sites I blogged about: https://www.artofthemystic.com/blog/deep-dream-and-gif-creator - but that was not it.
OK, I found it - called Newton Cradle: https://avatar.pho.to/newton_cradle/
there are many more effects: https://avatar.pho.to/
maybe I should edit my blog to include these sites.