This spell functions like
silent image, except that this spell's figment activates when a specific
condition occurs. The figment includes visual, auditory, olfactory, and thermal elements, including intelligible speech.
You set the triggering
condition (which may be a special word) when casting the spell. The event that triggers the illusion can be as general or as specific and detailed as desired but must be based on an audible, tactile, olfactory, or visual trigger. The trigger cannot be based on some quality not normally obvious to the senses, such as
alignment. (See
magic mouth for more details about such triggers.)