Similarly to magic mouth, Elminster's multiple mouths created a series of floating mouths that appeared on designated items or hung over one or more intended recipients known to, or at least seen by, the caster. The mouths delivered a message recorded by the caster at the time of casting and then disappeared. The spell worked regardless of the distance between caster and recipients, but only if they were located in the same plane of existence.
If only one recipient was specified, the mouths appeared in an encompassing circle and uttered their message in a chorus. For multiple recipients, all mouths appeared simultaneously in front of each of them and uttered their message at once.
The more powerful the caster, the more mouths could be created by the spell. Advanced wizards, upon performing a longer casting procedure, could create separate messages for each of the mouths, or even specify a delay between different mouths.
The message reproduced the caster's intonation, pauses, and volume. Although command words to activate magic items and verbal components of spells did not trigger the intended magical effects when uttered by the multiple mouths, they could be heard and learned by the recipient, who would then be able to use the words effectively.
The magic mouths produced by this spell normally appeared like bearded mouths with a dry voice, but their appearance could be changed. In particular, the Seven Sisters employed a variant that possessed ruby-red lips and spoke with husky voices.