"Well, when you learn a healing spell with four overlapping circles in a horseshoe shape you'll know it's the one I meant."
"The synesthesia spell is really amazing, though, if you've never felt moonlight and starlight on your skin you need to try it. Not to mention that you can taste sunbeams and listen to rainbows and--it's really, really, cool."
"That sounds really fun! Is it complicated or could I learn it soon?"
"Iiiiit's kinda complicated. But the target and the caster don't have to be the same! I could do it for you!"
"I don't know how much I'll like it... five minutes to start?"
"I can do that! What senses do you want converted exactly, to start, trying to do all of them as all the rest is way to overwhelming for your first time."
The sounds-that-are-images are distinct from regular sounds. If you just took the synesthetic sound of everything in your field of vision and played them all at once you would get a cacophony. This isn't that. Chords rise and fall as her gaze falls on this or that, faint melodies chirping out of the corners of her eyes. If she closes them, she gets a low steady soothing hum that is the darkness of her own eyelids.
"I know, right? Is there anything particularly beautiful you want to see before it wears off?"
"Uuuum, I want to go look at the sky and some plants... you know what I really want to hear is the stars at night but it's not night right now."
"Well, no, but there totally is the sky! Sort of. There's clouds!"
Clouds produce a sort of rolling leitmotif with variations and a harmony an octave down for the grey bits.
"Eeeeee! You're right, this spell is the most fun."
So Andrea is invited to Mehitabel's seventh birthday party.
"They don't look like magic until you activate them," she whispers, "so you can open them in front of people not in the know just fine."
"Good, my friends don't get to know yet," Mehitabel whispers back, and out loud she thanks everyone who gots her things and opens many books and a pair of shoes advertising non-slip grip and a bunch of hair scrunchies and a new raincoat and also her magic things.
Horace's magic thing is a complex wooden three-dimensional puzzle. Andrea's magic thing is a very nice digital watch in black with six rhinestones in the primary and secondary colors on the bezel.
Mehitabel thinks she knows what the watch maybe does and can't wait to find out about the puzzle! "Thank you so much!"