This seemed like a viable physics-math thread.
Sombody physics this for me.
"The object in the gif is primarily spinning around the long axis. BUT it also has just a bit of end-over-end spin that was accidentally introduced. It's not flipping back and forth; it's flipping end over end. The reason each flip is so sudden is due to the main spin."
I know that describing the "long axis" and "short axis" can be confusing and to be honest I'm not sure if the reddit guy got it right or wrong.. but anyway..
Also here's a bunch of good stuff from physics.stackexchange
Nice research! Also flipping things about the unstable axis so that they remain upright but now face away (phones remotes books baseball caps) may be about my favorite thing ever. Always wondered why it seemed easy to get that additional rotation in there and now science explains why!