when i eat the cactus i can see the sound waves, but i'm not sure that this is necissarily synesthesia.
i've def had synesthesia occur before, seeing music, hearing sights, etc.
but on the cactus i can literally see the sound waves come out of the speakers...or out of someone's mouth.
i saw an explaination of the siren effect (the doplar effect?) on the cactus as well...people were walking about 70 ft. in front of me, they were talking, but not very loud. i saw a 'cone' of sound waves come from there mouth into my ear, and their voices sounded very deep. when analyzing this (immediately thereafter) i realized that sound waves sound deeper when they're farther away...like with police sirens, and trains...deep when far away, higher when closer.
this observation of sound waves is really intense though, i went to school on a low dose of cactus (for shamanic practice of course

) . in class the teacher's voice was bouncing around the room, and i could hear it approaching my ears.
its like, normally you hear when the sound goes into your ear drum, but on cactus i am capable of seeing the sound approach my ear and slide down into the ear drum. it sounds like its coming down a tunnel actually.
thought i'd share this profound potential for the observation of physics..for it kind of relates to synesthesia. its just a very-clear form of it, no confusion of sensory input.