Boker Shaving Mug Thumb Hole ?

Hi.
Someone can tell me how this should be used?
https://www.bokerusa.com/shaving-mug-thu...o183?c=190
There's a sloped part with ridges, and a slot toward a lower part which is not visible from the pictures on the website.

Thanks!

I face-lather (so what do I know) but if I was going to use it, I’d probably rest it on my palm, put my thumb through the hole to secure it - create my lather on the side with the ridges, and rest my brush in the other half while I shaved …l but again - I have no idea how to use a scuttle or a mug.

I face-lather (so what do I know) but if I was going to use it, I’d probably rest it on my palm, put my thumb through the hole to secure it - create mt lather on the side with the ridges, and rest my brush in the other half while I shaved …l but again - I have no idea how to use a scuttle or a mug.

This is about it and does the one side have room for warm water for the brush to sit/soak. That's how vintage ones were setup I believe.
https://www.ebay.com/itm/235013870410?ha...R9KxtuKIYg

Thanks guys!
That makes a lot sense to me!

Best!
François