Chrysalis squinted at the board covered in barely legible notes and equations. "Syn-est-sia?"
"Synesthesia." Twilight corrected her, not looking up from what she was doing.
Chrysalis frowned and looked over at Twilight, who was still jotting down notes. "And just what in the Hive's name is Synthet...that."
Twilight's horn glowed a bit brighter before a book titled "Mental Disorders: From Aparoids to The Zero Virus" flipped open to the appropriate page and shoved itself in Chrysalis's face. "Synesthesia is a rare mental disorder wherein one perceives outside stimuli with the wrong sense. Symptoms include stuff like seeing sound, hearing colors, touching scents, et cetera." Chrysalis stepped back and took the book in her forelegs as Twilight went on. "I came across the disorder during some light research and my mind went back to our conversation before about the taste of emotions, so I thought-"
"Let me guess." Chrysalis sighed, shutting the book and setting it aside. "You want to induce the symptoms of such a disorder in yourself so as to perhaps taste love?"
"Exactly!" Twilight beamed, clearly delighted with herself. "I'm sure the experience will be very informative and intense. Just think of the potential cultural bridges that could be built if ponies could understand the changeling food pyramid and-"
"Stop." Chrysalis called, having put her face in her foreleg. Twilight was still in mid lecture and Chrysalis echoed herself loud enough to make herself heard. "Stop. Stop, stop, stopstopstop." Eventually Twilight obeyed as Chrysalis sighed again and made a counter clockwise motion with her other foreleg. "Just...rewind for a moment, Twilight."
Twilight tilted her head, finally looking at Chrysalis and finding herself rather surprised how irritated the changeling queen looked. "Is something wrong?"
"Is something wro-Where do I begin?" Chrysalis snapped, dragging her foreleg down her face before returning it to the ground. "Let's start with the basics. You want to intentionally perform a spell that will alter the way your mind perceives reality. Even for you, that seems remarkably foolhardy and dangerous."
Twilight narrowed her eyes, her coat bristling at the challenge. "It's not going to be permanent! The spell will last a minute at most before it wears off and I'll have Nurse Redheart and a few other doctors on standby if something goes awry. And besides, a little bit of danger is nothing new to me."
Chrysalis rolled her eyes, not impressed by this oh, so wonderful precaution. "Okay, assuming then that a minute 'at most' of intentionally warping your brain enough to see sounds or hear touch doesn't permanently damage your mind - which I feel I should note seems more than a little dangerous - let us not forget that even if your mind's senses are switched around, you still don't seem to have considered a few very important points to your little experiment."
"And what are those?" Twilight asked, her mind already pulling up a list of potential points Chrysalis might bring up and the counterpoints she would respond with. Chrysalis, knowing that expression, did much the same, aiming to poke at least as many holes in Twilight's plan as there were in one of her own legs.
"One; your species still does not perceive the emotional spectrum as a sense so there is nothing for it to switch with in terms of your senses." She closed her eyes. "Going back to our old metaphor of the sightless creature; altering the mind of a creature without eyes does not suddenly give them sight."
"Aha!" Twilight countered with a smirk. That one was number five on her list. "But we also agreed that a more apt metaphor was that ponies see in black and white while changelings see in color! Ergo, it is not an issue of giving a creature a sense it does not naturally possess, but one of expanding the scope of that sense for greater data input from outside stimuli through experimental procedures with disorders known to alter how a sense operates!" She beamed, quite pleased with her own brilliance. "Similarly, the issue of ponies not perceiving love as a sense, but as an emotion is rendered moot if we assume that love, as a changeling perceives it, is not the metaphysical emotion of love but an ambient source of energy that you can drain from a host when it is experiencing that particular type of chemical reaction perceived by the brain as the emotion love."
Chrysalis's jaw tightened as her point was countered but she kept up her smirk. "All right then, but that just brings me to my second point!" She pointed at Twilight. "Number two; you ponies lack the means to actually consume love as a changeling does. So even assuming your little spell does give you the means to perceive love as a source of energy for consumption - which given how you've explained this synes-whatever thing, I'm not quite convinced it will - how do you intend to acquire it's taste?"
"From you, obviously." Twilight replied, her eyes shining with mischief as Chrysalis raised an eyebrow. "You and I have been in a relationship for about a year now. I would hope then that I could trigger the chemical reaction of love in you and find a way to consume it from you."
Chrysalis threw back her head and laughed. "Oh, how very clever you are, Twilight. But you forget that were it possible to drain love from a changeling, we would have had little need to attempt a decapitation strike on Canterlot during Cadance's wedding." Twilight's smile faded a bit as Chrysalis went on. "I may not be able to explain how love tastes, but I can tell you for certain that while it is not impossible for a changeling to experience and reciprocate love, it is quite impossible for a changeling to feed another changeling with our love. Trust me, we've tried."
Twilight hesitated for just a moment, having honestly not accounted for such a scenario. Before she could rally, Chrysalis pressed her advantage. "And do not think that I missed you sidestepping the point about how you would drain the love from me. You only named me as a potential source of love for your experiment, you did not detail the means by which you would try to consume the love I would give off."
Twilight shut her eyes tight, thinking hard for a satisfying reply. With a spark, it clicked in her mind and she grinned. "Not so fast, Chrysalis. Do different kinds of love taste differently? Like romantic love versus familial love and such?"
Chrysalis rose an eyebrow at the question and smiled, curious enough to indulge the pony's line of questioning. "I suppose some varieties of love are more...nourishing than others, yes."
Twilight smiled, clapping her hooves together. "Then the issue of the source is solved! I shall invite my parents over to help me partake in the experiment as my source of love. That should work, right?" Chrysalis hummed in thought before nodding, conceding the point for the moment. "That just leaves how to consume it..." Twilight tapped her chin. "Well, how do you consume love Chrysalis? What's the process?"
Chrysalis smiled and shrugged in a not at all innocent but all to familiar fashion. "As I said before regarding the taste of love, it would be impossible to explain without-"
"A common frame of reference." Twilight finished with a scowl, scratching at the floor with her hooves and pacing. "So there isn't any way to really learn to drain love from somepony without being a changeling." She continued pacing as Chrysalis watched, fairly amused at seeing Twilight in her natural state of being. Nose deep in some problem and trying to sort it out. "I suppose I could chalk it up to a matter of trial and error and just having to learn to do it on my own. It'll likely take multiple castings of the Synesthsia Inducing Spell to refine it to do as I wish without side effects, so-"
Chrysalis laughed again, bringing Twilight's attention back to her. "Which, funnily enough brings me to my third point. Assuming that your parents are willing to participate in this experiment where you will be potentially putting yourself at risk in the name of tasting love and bridging cultural gaps, which is a bit of a leap. And assuming I'm willing to allow you to cast such a dangerous spell on yourself repeatedly without putting my foot down to make you stop, which is quite another leap. And finally assuming that you can discover though trial and error the means to consume your parent's love; how can you possibly be sure that what you experience and taste as love is accurate to how a changeling tastes it?" Twilight came to a full stop, working that over in her head as Chrysalis went on. "For all you know, the Sinestro-whatsit could give you a completely wrong interpretation of how love is perceived by my kind." She tapped her chin in idle thought. "What's a good metaphor? It would be like...giving a color blind creature the ability to see hues but it's all backwards and wrong."
"Which would defeat the purpose of the experiment as it would not be accurate to a changeling's perception of love." Twilight finished, looking a bit dejected now. "Darn. I thought I was really onto something there."
Chrysalis just smiled, coming over to pat Twilight on the head. "So close and yet so far, Princess." She winked. "Maybe one day I'll make you a proper changeling, then you can see as I see forever."
Twilight smiled back a bit. "You wouldn't dare."
Chrysalis rose a playful eyebrow. "Oh, wouldn't I?"
"No, you wouldn't." Twilight replied, leaning up to nuzzle her. "Because you are far too much of a pragmatist to lose your most stable source of food just to get a highly competent drone."
"Such modesty." Chrysalis rolled her eyes before nuzzling back. "But I suppose you are not wrong."