To clarify, this is how most transformation magic works, but very talented magicians like Ninni have found different ways to do this. For example, the magic bell from Petty Payback was based more on impromptu verbal cues. In that case, the bell "listens" for these cues, then uses the wearer's mental understanding of the cue to do the transformation. For example, if the wearer got called a cow, the spell would use the wearer's unconscious understanding of what a cow is to initiate the transformation.