This is the perk for being a pure level 5 Cultist sorcerer.
However, using it does nothing. You get the message that "this can only be used if you have an animal companion".
Therefore it's completely useless to a pure Sorcerer.
This might be a bug since perhaps it was intended to work on the Familiar, or on summons.
Apparently, I don't know how to respect forum rules. Oops! :(
Well? What is the point of telling me "there is a trick to it"? Is it some secret find out in-game thing?
Stop trolling people in forums, KOP. Either give them answers or keep quiet if you don't got anything valuable to add.
Now is there something specific here, or is this really a bug?
Changed it to bless instead of magic fang. You'll need a DM to help you out replacing the token.