They're minerals, Marie.
A red one. He took it from the mirror.
De vises stein. :0)
when do you use sten or stein? Is it just alternative spellings?
Yes, with "stein" being the most common.
how to say then: "what kind of stones does he have"?
The plural is "steiner", though you could use "stein" as a collective noun in this context.
In the audio it appears the "s" in "slags" makes the "sh" sound, like after an "r". Is this the case, or is it an error?
It's the case.
Both 'shlag' and 'slag' are correct pronunciation vice, though 'slag' is often considered to be quite posh, atleast in the Oslo-area. (I think I should mention that 'shlag' is not correct spelling)
I always heard that version with "sh" during my one year stay in Norway
What would you call whetting stones?
A whetting stone can be called "et bryne", "en hein", or "en brynestein".
A grindstone is "en slipestein".