I immediately found the mouse.
Close to the hidden door to the shrine, frozen pure white, dead.
I could see transparent violet teeth through its half-open mouth.
Teeth that were like magic stone.
I searched every corner of the room to make sure there wasn't a second one, made a box with earth magic, pierced the mouse's corpse with a rod, put it inside and completely sealed it.
I wonder if it would be better to dispose of the body with incineration.
Or if would be better to entrust it to the magic guild and have them study it.
The latter.
If I report it along with the information from the old man that it was magic stone disease, I'll be able to tell whether it really was.
Although in the first place, I don't know whether a virus can be obtained from a frozen corpse.