Good sportsmanship and you.

[Granyte the Ogre]

I'm with Nick 1000℅ on this. NPCs are usually asked before a mod "Who knows _____ sphere?" and are then sent out like that, if you claim to know a sphere and you miscant, the PCs have every right to call miscant just as an NPC has the right if a PC does the same. A simple "Miscant" and move on, NPCs get several pops and it's unfair to the PCs who might die in the same situation if NPCs can just say what they want and it works.

Again, be polite, don't be a douche about it. "Miscant" and move on.