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[Iacopo]

At 52 I started to floss my teeth, (better late than never), I bought various items for to see which ones could work better for me.
One of them is a dental floss holder, (by Gum), which I don't like very much for flossing, (I like more Ultraclean by Listerine for flossing molars), but I discovered that it is a good rattleback.  I try to spin whatever object happens in my hands, and this one was a surprise, I never saw a rattleback before.
It works only when spun in one direction.

https://www.youtube.com/watch?v=NdXrWKmWC94

[ta0]

  First unintentional rattleback I see! And such a unique rattleback shape! 
Congratulations on discovering this! I spin lots of stuff but probably would have not spun that on its side.

[Jeremy McCreary]

I try to spin whatever object happens in my hands, and this one was a surprise, I never saw a rattleback before.
It works only when spun in one direction.

Excellent find! I have the same spinning obsession. Guessing a lot of other forum members do, too. Maybe it's neurological.

A wonderful talk by Tadashi Takieda on "chiral dynamics", exploring first the one-way motion of the rattleback, then the inverting motion of the standard tippe top, and then the odd behavior of a special tippe top that inverts when you spin it in one direction but not the other!

https://youtu.be/x8WazFUIbow

[Iacopo]

A wonderful talk by Tadashi Takieda on "chiral dynamics"

Many things to think about.  I found interesting the seal making the ball to spin too.

[the Earl of Whirl]

A dental floss holder rattleback!  Who could have imagined this?  Good discovery!!!

[ta0]

Somebody tried to optimize a Rattleback using SolidWorks. The results are not too impressive (I prefer Iacopo's flossing rattleback), but there are some good points about how it works:
https://www.goengineer.com/blog/understanding-rattleback-mystery-solidworks-motion

[ortwin]

Thank you ta0!
I am happy that your post today  made me aware of this thread!
I did not follow the link that you provided today, BUT:

• I am using since a few years that flossholder Iacopo is showing in the first post, but I have never given it a spin yet.
• I enjoyed the lecture of Tadashi Takieda that Jeremy posted very much (it has even Eulers disk in it)

[ta0]

Tim covers a lot of different rattleback on this video, including some unintentional ones:

https://www.youtube.com/watch?v=11NHjiEYnI0