Inform Artemis of any new findings regarding the book? That could be done, and Casimir saw no reason to withhold any informatjon from the young teenager. He agreed by shaking his head, then also mentioned he would expect Art to do the same. 
As soon as both the Slytherins agreed on their terms, the book reacted. Glowing an eerie green and changing before their eyes, the title now read "Introduction to the Dark Arts". See, now this was starting to speak Casimir's language. He had a handful of spells at his disposal that were called "dark" every now and then, but never anything on this scale.

"Oooh...."

Casimir felt the cover of the book with his fingers. A most intriguing book indeed. It occurred to him that letting others see it would be risky, especially those like Grace from the Hufflepuff house, or even the shy girl Willow. That girl came from a family of aurors, and Casimir honestly didn't feel like dealing with "warriors of light" when he was this close to secret knowledge. Using his wand, he made sure the door to their compartment was closed, and cast a small spell on it that would alert him and Artemis whenever someone touched the door with the intent to open it.

"We're going to have to keep this under wraps, so make sure you keep this in a safe place."