CapnZapp
Legend
Thanks 
Yes, I wouldn't have intelligent creatures know they have the cantrip just from being in the skull's vincinity. Unintelligent creatures is another matter...
Intelligent creatures would only feel a tingle, a bilge in their throat.
A spellcaster or other individual trained in Arcana (etc) that sees his foes start spewing poison would be able to deduce what's going on, and to start using the cantrip herself.
Otherwise, the winning side can examine the skull per your campaign's normal magic-identifying rules.
For undead and beasts and the like, I will make the use of the cantrip into a reflex: the monster can start using the cantrip immediately. Of course, the skull does not force anyone to use it. Even zombies and amoebas could choose to use their regular attacks over Poison Spray if that benefited them more.

Yes, I wouldn't have intelligent creatures know they have the cantrip just from being in the skull's vincinity. Unintelligent creatures is another matter...
Intelligent creatures would only feel a tingle, a bilge in their throat.
A spellcaster or other individual trained in Arcana (etc) that sees his foes start spewing poison would be able to deduce what's going on, and to start using the cantrip herself.
Otherwise, the winning side can examine the skull per your campaign's normal magic-identifying rules.
For undead and beasts and the like, I will make the use of the cantrip into a reflex: the monster can start using the cantrip immediately. Of course, the skull does not force anyone to use it. Even zombies and amoebas could choose to use their regular attacks over Poison Spray if that benefited them more.