All the way back to Alphys's lab.
The True Lab, as we know, is where Alphys created the amalgamates. This one done by extracting "determination" from the human souls that Asgore collected by using a machine that she MIGHT HAVE invented (emphasis on "might have," please, don't scream in the comments that Dr. Gaster created it).
It is also extremely likely that she brought Flowey to life, as hinted in a few lab entries that she (more than likely) wrote. This also was done by injecting an object with determination (which, in this case, happened to be a golden flower).
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🔅 F L O W E R - F E L T E M O T I O N S 🔅
If this is true, then why do we see moments where he seems to be feeling things?
Not just the resilience towards death; but also in cases such as: when he shakes in fear during the genocide run, maniacal laughter when he traps you at the start of the game, or even just the nervousness when everyone encourages us before he turns into Asriel!
If he is truly emotionless, why would he act this way? Simple: he CAN feel, just that his feelings aren't strong (especially without his own monster soul).
Strem, how this this possible?
To figure this out, we must review his backstory; even further back than from when he popped out of the garden.
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My response to why Flowey has emotions is because he was injected with something that CAN feel.
The determination comes from SOULs; souls that gave children life and feeling. Part of that was extracted from the human souls, and placed into this gold-petaled embodiment. That extraction is what gives him a weak sense of emotion.
So, next time, instead of thinking he doesn't care, look into those demented eyes again. Maybe (just maybe) there will be a way to save this flower in the future.
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❤️ 💉 ❤️🔅 C O N C L U S I O N 🔅
Well, that was my take on why our vicious antagonist can feel! What about you; anything to add? A debunking or review? Go ahead and comment it below (with wit and reason, don't just say, "Your theory sucks, and is wrong!.